Unify plugin endpoint configuration for api and worker: An alternative solution to PR #13214

[BorisPolonsky]

Unify plugin endpoint configuration for api and worker by adopting PLUGIN_DAEMON_URL/PLUGIN_DAEMON_KEY and removing PLUGIN_API_URL/PLUGIN_API_KEY to avoid confusion.
This is an alternative solution to #13214, which does things the other way around.

Fixes #13113

Summary

PR #13055 introduces PLUGIN_API_URL and PLUGIN_API_KEY in docker-compose.yaml, which coexists with the original PLUGIN_DAEMON_URL and PLUGIN_DAEMON_KEY (the ones that actually take effect) and caused confusions that ends up in InternalServerError (#12664). This PR and the alternative solution #13214 aims to unify these two settings.

Tip

Close issue syntax: Fixes #<issue number> or Resolves #<issue number>, see documentation for more details.

Screenshots

Before	After
...	...

Checklist

Important

Please review the checklist below before submitting your pull request.

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[Yeuoly]

LGTM