feat: add GitLab to PR generator for applicationset

[iverberk]

Closes #9262

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Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes: ApplicationSet Pull Request Generator for GitLab #9262 (Created by Spork)
• The title of the PR states what changed and the related issues number (used for the release note).
• I've included "Closes [ISSUE #]" or "Fixes [ISSUE #]" in the description to automatically close the associated issue.
• I've updated both the CLI and UI to expose my feature, or I plan to submit a second PR with them.
• Does this PR require documentation updates?
• I've updated documentation as required by this PR.
• Optional. My organization is added to USERS.md.
• I have signed off all my commits as required by DCO
• I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• My build is green (troubleshooting builds).

[codecov]

Codecov Report

Merging #9264 (347bf29) into master (3337616) will increase coverage by 0.02%.
The diff coverage is 72.50%.

@@            Coverage Diff             @@
##           master    #9264      +/-   ##
==========================================
+ Coverage   45.73%   45.75%   +0.02%     
==========================================
  Files         220      221       +1     
  Lines       26006    26046      +40     
==========================================
+ Hits        11893    11917      +24     
- Misses      12456    12469      +13     
- Partials     1657     1660       +3     

Impacted Files	Coverage Δ
applicationset/generators/pull_request.go	39.13% <0.00%> (-3.73%)	⬇️
...is/applicationset/v1alpha1/applicationset_types.go	34.69% <ø> (ø)
applicationset/services/pull_request/gitlab.go	85.29% <85.29%> (ø)
applicationset/services/scm_provider/github.go	75.29% <0.00%> (-5.89%)	⬇️

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[rishabh625]

Thanks

LGTM!! , just a nitpick if u feel to change then do it

Document the functions and change this function name

[iverberk]

I've kept the function name consistent with the existing pull request services (Github, gitea, bitbucket, etc.). What would you suggest in terms of an alternative name?

[RuBiCK]

Is there any ETA for this feature?

[crenshaw-dev]

Just one small nit. :-)

[crenshaw-dev]

@RuBiCK by default, this would end up in 2.5. If you need it in 2.4, I can check with folks about cherry-picking it back.

[RuBiCK]

@crenshaw-dev that is what we need to create ephemeral environments.
If it could be implemented in 2.4 it will be really amazing.

[crenshaw-dev]

@RuBiCK I'll bring it up in the contributor meeting today. https://docs.google.com/document/d/1xkoFkVviB70YBzSEa4bDnu-rUZ1sIFtwKKG1Uw8XsY8/edit

[crenshaw-dev]

@RuBiCK the consensus from the contributors is that we should protect the RC and save this feature for 2.5.

If you need this feature super soon, it should be easy enough to cherry-pick onto a custom build.

[RuBiCK]

@crenshaw-dev thanks for bringing that up in the meeting, I really appreciate it.

In the beginning, I thought it was an undocumented feature because it's mentioned in the documentation and I thought It would be already included and documented for 2.4.

In my company, we do not program in GO and I'm not a developer, but I'll try to find someone to help me build this version because It's crucial for the company this feature to adopt Argocd.

[crenshaw-dev]

In the beginning, I thought it was an undocumented feature because it's mentioned in the documentation and I thought It would be already included and documented for 2.4.

Ah yep, we need to remove that. I'm not sure how it got there.

The basic steps of building this internally are:

1. clone the argo-cd repo and checkout the branch for the release you want to run (release-2.4 probably)
2. git cherry-pick COMMIT onto that branch, where COMMIT is the commit has for this PR (that commit hash will appear on this PR after I merge it)
3. make image IMAGE_TAG=2.4-plus-gitlab
4. docker push that tag to your internal artifact repo
5. update your Argo CD install manifests to use that image for the appset controller (no need to update the other images)
6. kubectl apply the applicationset CRD manifest from this PR to the cluster where you need gitlab support

[crenshaw-dev]

Thanks!