update compose file

[Savy011]

This PR fixes the race-condition where the backends start before the db container, resulting in the backend panicking and exiting early.

what does this do?

• add health check for db server
• start backend only after the health-check for db passes
  • add a restart so that the backend keeps re-starting itself in case of errors (unless stopped by the user)
• create a network bridge to connect backend and db
• remove exposing db's network ports.
• move database and smtp credentials to .env file instead of hardcoding.
• update readme to include frontend development instructions

how to test?

• Compose file changes
  1. clone the repo
  2. checkout savy/compose branch
  3. set required env vars
  4. run docker compose up to run the container.
     • Optionally pass the -d flag to run the container in daemon mode.
  5. the backend should be running and listen for requests at port 8080
• README updates
  1. just open the readme and check For Frontend Development (Docker) section

[GURMEHAR-PEC]

All good, approved