Add pipeline author and avatar env vars

[qwerty287]

#4626 (comment)

[woodpecker-bot]

Deploying preview to https://woodpecker-ci-woodpecker-pr-5227.surge.sh

[codecov]

Codecov Report

Attention: Patch coverage is 42.85714% with 4 lines in your changes missing coverage. Please review.

Project coverage is 26.35%. Comparing base (a02de81) to head (1d1ff31).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
pipeline/frontend/metadata/environment.go	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5227      +/-   ##
==========================================
- Coverage   26.36%   26.35%   -0.02%     
==========================================
  Files         401      401              
  Lines       28537    28543       +6     
==========================================
- Hits         7525     7522       -3     
- Misses      20323    20332       +9     
  Partials      689      689              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[pat-s]

What use case does the avatar have?

While it's surely not harming, it extends the list and makes it bigger without a real use case (?).

[qwerty287]

@6543 suggested it in #4626

unsure about the necessity

[qwerty287]

Can we get a decision here? I don't care tbh. @6543 what do you say? You originally suggested this.

[xoxys]

Also not sure about the use case but its just an env var and it doesnt increase the code complexity so why not.

[anbraten]

I've searched for it and saw it being used by notification plugins to show the author and their avatar

[nmapx]

Have you noticed it overrides the commit author? I don't know if that's how it supposed to work, looks weird.
If you trigger the pipeline manually on a commit that you did not pushed it's gonna say that "prev commit author" is the person that actually pushed the commit woodpecker is actually processing.