Allow containers/plugins to generate outputs

[qwerty287]

Clear and concise description of the problem

The only way for a plugin or another container to communicate to other containers or with the build process is to create files in the repository, which is a bad idea.

Suggested solution

A way for plugins or even containers to generate outputs which can be accessed from other containers or the users. Similar to GitHub Actions: https://docs.github.com/en/actions/using-jobs/defining-outputs-for-jobs

Alternative

No response

Additional context

depends on #2954

Validations

• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

[6543]

The only other generic way beside created files would be to expose an api via some socket (unix socet or udp/tcp ...)

And indicate that via some env var

[qwerty287]

I also think that's the best and most clean solution. Creating files could be easier to implement though (both woodpecker and plugin side)

[6543]

-> #2954

[6543]

PS: as github actions are mentioned here, i like the current architecture that divides pipelime frontemd from backend. Do validations on steps after a step did run will break this.

[6543]

A backchannel also would be usefull for #2282 and so on.

[6543]

Note: we should generate some sort of temporar tocken on the agent for each workflow, so you can make sure to not let other workflows malicious or unintendet interfear with things

[6543]

(Or if falsly exposed externaly)