Cleanup and update environment variables configuration

The environment variables setup in the Resonate Backend seems outdated and may not fully match the variables used in the codebases this creates confusion for new contributions and can cause setup errors...

Problems Identified
1- .env.example is missing some environment variables used in the code
2- some variables in .env.example may be unused or deprecated
3- naming format is inconsistent
4- no comments explaining what each variable is for

Proposed fix

1- review all environment variables references in the codebase
2- update .env.example with all required keys
3- remove unused or outdated variables
4- add comments for clarity
5- ensure consistent naming

This Matters because-
1- helps new contributors set up the project easily
2- prevents configuration errors
3-improves documentation