fix: Redis rdb persistance | User session persistance (#19981)

## Description
- Updated redis.conf to set the Redis rdb directory to
`/appsmith-stacks/data/redis` bind-mount directory, so that the data is
persisted after the container restarts/updates. ( This was causing user
sessions on Appsmith installations using the embedded Redis to reset
after every container restart, since the redis data was not being
persisted)
- Updated redis.conf for the embedded Redis to increase the snapshot
frequency to dump after every 15 sec if at least 1 key changed

Fixes #19768

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


## How Has This Been Tested?
- Manual

deploy/docker/entrypoint.sh

@@ -248,8 +248,14 @@ configure_supervisord() {
     fi
     if [[ $APPSMITH_REDIS_URL == *"localhost"* || $APPSMITH_REDIS_URL == *"127.0.0.1"* ]]; then
       cp "$SUPERVISORD_CONF_PATH/redis.conf" /etc/supervisor/conf.d/
+      # Initialize Redis rdb directory
+      local redis_db_path="$stacks_path/data/redis"
+      mkdir -p "$redis_db_path"
       # Enable saving Redis session data to disk more often, so recent sessions aren't cleared on restart.
-      sed -i 's/^# save 60 10000$/save 60 1/g' /etc/redis/redis.conf
+      sed -i \
+        -e 's/^save 60 10000$/save 15 1/g' \
+        -e "s|^dir /var/lib/redis$|dir ${redis_db_path}|g" \
+        /etc/redis/redis.conf
     fi
     if ! [[ -e "/appsmith-stacks/ssl/fullchain.pem" ]] || ! [[ -e "/appsmith-stacks/ssl/privkey.pem" ]]; then
       cp "$SUPERVISORD_CONF_PATH/cron.conf" /etc/supervisor/conf.d/