feat: add short_sha_7 to AppSet generators (#11976)

[fty4]

Hello everyone,

as in issue #11976 discussed a 7 character sha would help some users to use AppSets.
Therefore this PR will add a 7 character key to use it in the ApplicationSet.

Following keys are added:

Generator PR

• head_short_sha_7

Generator SCM provider

• short_sha_7

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.
• The title of the PR states what changed and the related issues number (used for the release note).
• The title of the PR conforms to the Toolchain Guide
• 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.
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• I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
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• My new feature complies with the feature status guidelines.
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Please see Contribution FAQs if you have questions about your pull-request.

closes #11976

Marco Lecheler marco.lecheler@mercedes-benz.com Mercedes-Benz Tech Innovation GmbH (ProviderInformation)

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.01 🎉

Comparison is base (9b53eeb) 49.05% compared to head (126a821) 49.06%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #13199      +/-   ##
==========================================
+ Coverage   49.05%   49.06%   +0.01%     
==========================================
  Files         246      246              
  Lines       42569    42581      +12     
==========================================
+ Hits        20882    20894      +12     
  Misses      19572    19572              
  Partials     2115     2115              

Impacted Files	Coverage Δ
applicationset/generators/pull_request.go	52.23% <100.00%> (+2.23%)	⬆️
applicationset/generators/scm_provider.go	34.19% <100.00%> (+2.64%)	⬆️

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