chore: Set statement timeout for Postgres (#6641)

By default, Rails does not set a timeout on database statements. For example, this will run for a full day, even if your ruby process goes away. But it's configurable in the database.yml with the statement_timeout variable.

Hence we are enforcing a 14s timeout by default. Migration commands inside chatwoot will run with a 10 minutes timeout. For specific cases like migrations, we can override this timeout using the environment variable POSTGRES_STATEMENT_TIMEOUT while starting a new rails console.

Test the timeouts from the rails console using.

```
ActiveRecord::Base.connection.execute("SELECT pg_sleep(15);")
```

ref: https://github.com/ankane/the-ultimate-guide-to-ruby-timeouts#postgresql
ref: https://til.hashrocket.com/posts/b44baf657d-railspg-statement-timeout-

.env.example

@@ -52,6 +52,8 @@ POSTGRES_HOST=postgres
 POSTGRES_USERNAME=postgres
 POSTGRES_PASSWORD=
 RAILS_ENV=development
+# Changes the Postgres query timeout limit. The default is 14 seconds. Modify only when required.
+# POSTGRES_STATEMENT_TIMEOUT=14s
 RAILS_MAX_THREADS=5
 
 # The email from which all outgoing emails are sent