Document pipeline backend engine interface precisely

[6543]

Changes:

• Document pipeline backend engine interface precisely
• Add debug log to docker backend on ContainerWait return values

[6543]

use:

go doc go.woodpecker-ci.org/woodpecker/v3/pipeline/backend/types.Backend

to generate the golang doc string

[codecov]

Codecov Report

❌ Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 19.81%. Comparing base (9edaa1e) to head (5aa2a05).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pipeline/backend/docker/docker.go	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5583      +/-   ##
==========================================
- Coverage   19.81%   19.81%   -0.01%     
==========================================
  Files         420      420              
  Lines       39820    39823       +3     
==========================================
- Hits         7891     7889       -2     
- Misses      31220    31226       +6     
+ Partials      709      708       -1     

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[qwerty287]

Thanks

[6543]

as we now have a good description of expections .... we should check our backends.

the local backend does not match that so fix is here: #5582