ci(gitops-engine): support tagged releases for gitops-engine

[rumstead]

closes #27725

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 Title of the PR
• 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.
• 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).
• My new feature complies with the feature status guidelines.
• I have added a brief description of why this PR is necessary and/or what this PR solves.
• Optional. My organization is added to USERS.md.
• Optional. For bug fixes, I've indicated what older releases this fix should be cherry-picked into (this may or may not happen depending on risk/complexity).

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.88%. Comparing base (3a2e2f6) to head (873bf01).
⚠️ Report is 6 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #27740   +/-   ##
=======================================
  Coverage   63.88%   63.88%           
=======================================
  Files         421      421           
  Lines       57657    57657           
=======================================
+ Hits        36834    36836    +2     
+ Misses      17363    17362    -1     
+ Partials     3460     3459    -1     

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[Copilot]

Pull request overview

This PR addresses downstream Go module resolution failures by moving Argo CD’s github.com/argoproj/argo-cd/gitops-engine dependency toward using a tag that can be fetched outside this repo (instead of an invalid/unstable pseudo-version), and by extending the release automation to create and reference a path-prefixed gitops-engine tag.

Changes:

• Update root go.mod to a new gitops-engine pseudo-version and document the intent to use path-prefixed tags.
• Extend the release workflow to publish a gitops-engine/<tag> tag alongside the Argo CD release tag.
• Extend the init-release workflow to rewrite the gitops-engine requirement in go.mod to the release tag version during release preparation.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
go.mod	Updates the required gitops-engine version and documents the intended tag scheme for downstream consumption.
.github/workflows/release.yaml	Adds logic to create/push a path-prefixed gitops-engine tag during the post-release steps.
.github/workflows/init-release.yaml	Adds automation to rewrite the gitops-engine require entry to a release tag during release branch prep.

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