fix: Fetch app's current branch from redux store (#20601)

## Description

### Cause of issue

Appsmith's persistent data is stored in the browser's localStorage under
a key generated using the `applicationId` and `branch name`. When
fetching the store's value on page load, if the branch's name is not
present in the URL string, its value defaults to an emptyString.

### Solution
Default value of `branch name` should be the current git branch.

Fixes #15692 
## Type of change

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


## How Has This Been Tested?
manual

### Test Plan
Cypress covers test case

### Issues raised during DP testing
> Link issues raised during DP testing for better visiblity and tracking
(copy link from comments dropped on this PR)


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


### QA activity:
- [ ] Test plan has been approved by relevant developers
- [ ] Test plan has been peer reviewed by QA
- [x] Cypress test cases have been added and approved by either SDET or
manual QA
- [ ] Organized project review call with relevant stakeholders after
Round 1/2 of QA
- [x] Added Test Plan Approved label after reveiwing all Cypress test

app/client/cypress/support/Pages/GitSync.ts

@@ -35,7 +35,7 @@ export class GitSync {
   }
 
   CreateNConnectToGit(
-    repoName: string = "Test",
+    repoName = "Test",
     assertConnect = true,
     privateFlag = false,
   ) {
@@ -129,7 +129,7 @@ export class GitSync {
     });
   }
 
-  CreateGitBranch(branch: string = "Test", toUseNewGuid = false) {
+  CreateGitBranch(branch = "Test", toUseNewGuid = false) {
     if (toUseNewGuid) this.agHelper.GenerateUUID();
     this.agHelper.AssertElementExist(this._bottomBarCommit);
     this.agHelper.GetNClick(this._branchButton);

app/client/src/entities/Engine/index.ts

@@ -16,6 +16,7 @@ import history from "utils/history";
 import URLRedirect from "entities/URLRedirect/index";
 import URLGeneratorFactory from "entities/URLRedirect/factory";
 import { updateBranchLocally } from "actions/gitSyncActions";
+import { getCurrentGitBranch } from "selectors/gitSyncSelectors";
 
 export type AppEnginePayload = {
   applicationId?: string;
@@ -69,7 +70,14 @@ export default abstract class AppEngine {
     if (!apiCalls)
       throw new PageNotFoundError(`Cannot find page with id: ${pageId}`);
     const application: ApplicationPayload = yield select(getCurrentApplication);
-    yield put(updateAppStore(getPersistentAppStore(application.id, branch)));
+    const currentGitBranch: ReturnType<typeof getCurrentGitBranch> = yield select(
+      getCurrentGitBranch,
+    );
+    yield put(
+      updateAppStore(
+        getPersistentAppStore(application.id, branch || currentGitBranch),
+      ),
+    );
     const toLoadPageId: string = pageId || (yield select(getDefaultPageId));
     this._urlRedirect = URLGeneratorFactory.create(
       application.applicationVersion,