add branch-allowlist repo-config parameter

[Steffen911]

Context

Fixes #1028

What

This PR should add a branch_allowlist parameter to the RepoConfig that comes into effect in combination with the mergeable requirement.
In addition to checking if a PR is mergeable it also validates that it targets a set of allowed base branches.
Otherwise one might avoid the mergeable requirement by planning and applying on a non-protected branch.

Example

I set branch_allowlist: [master] and tried to apply a PR that is targeting the development branch. Error message:

Looking forward to all reviews :-)

[codecov]

Codecov Report

Merging #1292 (84ba0d1) into master (eaafd43) will decrease coverage by 0.03%.
The diff coverage is 62.50%.

@@            Coverage Diff             @@
##           master    #1292      +/-   ##
==========================================
- Coverage   70.00%   69.97%   -0.04%     
==========================================
  Files          74       74              
  Lines        5585     5606      +21     
==========================================
+ Hits         3910     3923      +13     
- Misses       1312     1319       +7     
- Partials      363      364       +1     

Impacted Files	Coverage Δ
server/events/models/models.go	78.99% <ø> (ø)
server/events/yaml/raw/global_cfg.go	0.00% <0.00%> (ø)
server/events/yaml/valid/repo_cfg.go	21.42% <ø> (ø)
server/events/yaml/valid/global_cfg.go	87.26% <60.00%> (-2.40%)	⬇️
server/events/project_command_runner.go	72.97% <66.66%> (-0.37%)	⬇️
server/events/project_command_builder.go	79.01% <100.00%> (+0.08%)	⬆️
server/events/yaml/raw/project.go	100.00% <100.00%> (ø)

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[nishkrishnan]

👋 Thanks for contributing!

By writing e2e tests/running the server you should be able to figure out if there are other places to modify.

[Steffen911]

@nishkrishnan Thank you for your comment. I ran the commands locally with a test repository and confirmed that it works as expected now.

As soon as the code logic is reviewed I can also take care of the documentation, but I'd prefer to split the PRs to keep their size manageable.

[pinkavaj]

This one might be in conflict with #1383

The mentioned MR looks a little bit more generic and also clear and simpler for me.

[nishkrishnan]

This one might be in conflict with #1383

The mentioned MR looks a little bit more generic and also clear and simpler for me.

I agree.

[nishkrishnan]

Closing this in favor of: #1383