fix: Changed error message to be thrown on failed parsing of executeActionDTO (#23321)

## Description
> A malformed body (multipart form) for the /execute endpoint leads to
an error on UI showing: "invalid parameter: executeActionDTO".
> This has now been changed in this pr to show error as: "The request
could not be understood by the server due to malformed syntax."

#### PR fixes following issue(s)
Fixes #23250 (partly)

#### Type of change
- Bug fix (non-breaking change which fixes an issue)

## Testing
>
#### How Has This Been Tested?
> Please describe the tests that you ran to verify your changes. Also
list any relevant details for your test configuration.
> Delete anything that is not relevant
- [ ] Manual
- [ ] Jest
- [ ] Cypress
>
>
#### Test Plan
> This can be tested by calling /execute endpoint with malformed form
data since replicating this issue using UI is unreliable. The UI in
general doesn't produce a malformed request body.

## Checklist:
#### Dev activity
- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my own code
- [x] I have commented my code, particularly in hard-to-understand areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [ ] PR is being merged under a feature flag


#### QA activity:
- [ ] [Speedbreak
features](https://github.com/appsmithorg/TestSmith/wiki/Test-plan-implementation#speedbreaker-features-to-consider-for-every-change)
have been covered
- [ ] Test plan covers all impacted features and [areas of
interest](https://github.com/appsmithorg/TestSmith/wiki/Guidelines-for-test-plans/_edit#areas-of-interest)
- [ ] Test plan has been peer reviewed by project stakeholders and other
QA members
- [ ] Manually tested functionality on DP
- [ ] We had an implementation alignment call with stakeholders post QA
Round 2
- [ ] Cypress test cases have been added and approved by SDET/manual QA
- [ ] Added `Test Plan Approved` label after Cypress tests were reviewed
- [ ] Added `Test Plan Approved` label after JUnit tests were reviewed

app/server/appsmith-server/src/main/java/com/appsmith/server/exceptions/AppsmithError.java

@@ -82,6 +82,7 @@ public enum AppsmithError {
     ACL_NO_RESOURCE_FOUND(404, AppsmithErrorCode.ACL_NO_RESOURCE_FOUND.getCode(), "Unable to find {0} {1}. Either the asset doesn''t exist or you don''t have required permissions",
             AppsmithErrorAction.DEFAULT, "No resource found or permission denied", ErrorType.INTERNAL_ERROR, null),
     GENERIC_BAD_REQUEST(400, AppsmithErrorCode.GENERIC_BAD_REQUEST.getCode(), "Bad request: {0}", AppsmithErrorAction.DEFAULT, "Invalid request", ErrorType.BAD_REQUEST, null),
+    GENERIC_REQUEST_BODY_PARSE_ERROR(400, AppsmithErrorCode.MALFORMED_REQUEST.getCode(), "Server cannot understand the request, malformed payload. Contact support for help.", AppsmithErrorAction.DEFAULT, "Malformed request body", ErrorType.BAD_REQUEST, null),
     VALIDATION_FAILURE(400, AppsmithErrorCode.VALIDATION_FAILURE.getCode(), "Validation Failure(s): {0}", AppsmithErrorAction.DEFAULT, "Validation failed", ErrorType.INTERNAL_ERROR, null),
     INVALID_CURL_COMMAND(400, AppsmithErrorCode.INVALID_CURL_COMMAND.getCode(), "Invalid cURL command, couldn''t import.", AppsmithErrorAction.DEFAULT, "Invalid cURL command", ErrorType.ARGUMENT_ERROR, null),
     INVALID_LOGIN_METHOD(401, AppsmithErrorCode.INVALID_LOGIN_METHOD.getCode(), "Please use {0} authentication to login to Appsmith", AppsmithErrorAction.DEFAULT, "Invalid login method", ErrorType.INTERNAL_ERROR, null),

app/server/appsmith-server/src/main/java/com/appsmith/server/exceptions/AppsmithErrorCode.java

@@ -64,6 +64,7 @@ public enum AppsmithErrorCode {
     GOOGLE_RECAPTCHA_TIMEOUT("AE-APP-5042", "Google recaptcha timeout"),
     NAME_CLASH_NOT_ALLOWED_IN_REFACTOR("AE-AST-4009", "Name clash not allowed in refactor"),
     GENERIC_BAD_REQUEST("AE-BAD-4000", "Generic bad request"),
+    MALFORMED_REQUEST("AE-BAD-4001", "Malformed request body"),
     GOOGLE_RECAPTCHA_FAILED("AE-CAP-4035", "Google recaptcha failed"),
     INVALID_CRUD_PAGE_REQUEST("AE-CRD-4039", "Invalid crud page request"),
     EMPTY_CURL_INPUT_STATEMENT("AE-CRL-4054", "Invalid CURL input statement"),

app/server/appsmith-server/src/main/java/com/appsmith/server/solutions/ce/ActionExecutionSolutionCEImpl.java

@@ -306,7 +306,7 @@ public class ActionExecutionSolutionCEImpl implements ActionExecutionSolutionCE
                         return Mono.just(objectMapper.readValue(byteData, ExecuteActionDTO.class));
                     } catch (IOException e) {
                         log.error("Error in deserializing ExecuteActionDTO", e);
-                        return Mono.error(new AppsmithException(AppsmithError.INVALID_PARAMETER, EXECUTE_ACTION_DTO));
+                        return Mono.error(new AppsmithException(AppsmithError.GENERIC_REQUEST_BODY_PARSE_ERROR));
                     }
                 })
                 .flatMap(executeActionDTO -> {

app/server/appsmith-server/src/test/java/com/appsmith/server/solutions/ce/ActionExecutionSolutionCEImplTest.java

@@ -205,7 +205,7 @@ class ActionExecutionSolutionCEImplTest {
         StepVerifier
                 .create(actionExecutionResultMono)
                 .expectErrorMatches(e -> e instanceof AppsmithException &&
-                        e.getMessage().equals(AppsmithError.INVALID_PARAMETER.getMessage("executeActionDTO")))
+                        e.getMessage().equals(AppsmithError.GENERIC_REQUEST_BODY_PARSE_ERROR.getMessage()))
                 .verify();
     }
 
@@ -407,5 +407,4 @@ class ActionExecutionSolutionCEImplTest {
                 })
                 .verifyComplete();
     }
-
 }