API resource refactoring

[tom2drum]

Description and Related Issue(s)

• Split resource declarations into separate files and prefix them based on the API they belong to.
• In the app configuration, consolidate all external API parameters in one location for easier management.

These changes will facilitate future refactoring of Rewards API calls, ensuring that all necessary headers are passed in one place using the useApiFetch hook.

Checklist for PR author

• I have tested these changes locally.
• I added tests to cover any new functionality, following this guide
• Whenever I fix a bug, I include a regression test to ensure that the bug does not reappear silently.
• If I have added, changed, renamed, or removed an environment variable
  • I updated the list of environment variables in the documentation
  • I made the necessary changes to the validator script according to the guide
  • I added "ENVs" label to this pull request