ci: convert release builder to workflow_dispatch (v0.36)

[sydorovdmytro]

Part of the DEVOPS-1050 phase-4 fan-out (loft-sh/vcluster legacy line). Builder-only conversion, sibling to vcluster#4073–#4077 (v0.31–v0.35).

What

Converts only the builder release.yaml:

• Drops the release:created trigger; the workflow is dispatched via workflow_dispatch --ref <tag>, so github.ref/github.ref_name carry the version.
• Decouples github.event.release.tag_name → github.ref_name in check_minimum_version_tag and the failure Slack notification.
• Derives previous_tag from branch-local history (git describe --tags --abbrev=0 --match 'v*' "${GITHUB_SHA}^") instead of git rev-list --tags --skip=1, which picks the global latest tag (wrong on a release branch).

Validators intentionally unchanged

Legacy lines get no post-build validation wired — matches current behavior (no regression). Release validation for new lines (>= v0.37) is handled by main's tag-dispatched validators (reference PR vcluster#4072).

v0.36 is still the old (pre-monorepo) layout, so this is identical to the v0.35 conversion (#4073) apart from a pre-existing base delta (linear-release-sync tag bump) the conversion does not touch.

Actionlint-clean. Draft to match the sibling PRs.

---

Note

Medium Risk
Changes how production releases are triggered and how Goreleaser’s previous tag is chosen; mis-dispatch or a bad previous_tag could block releases or skew release notes, but no app runtime or security paths are touched.

Overview
Part of DEVOPS-1050: the release.yaml builder no longer runs on release:created. It is started with gh workflow run release.yaml --ref <tag>, so the version comes from github.ref / github.ref_name instead of github.event.release.tag_name (minimum-version check, checkout ref, failure Slack notify).

previous_tag is now computed with git describe from ${GITHUB_SHA}^ on the current branch, replacing the global “second-latest tag” lookup so Goreleaser’s GORELEASER_PREVIOUS_TAG / changelog baseline is correct on release branches.

Comments document that the GitHub Release is produced at the end of a green build, avoiding monorepo OSS releases re-firing this workflow.

^{Reviewed by Cursor Bugbot for commit b8ad370. Bugbot is set up for automated code reviews on this repo. Configure here.}

[github-actions]

E2E Ginkgo Tests

Status	Commit	Run
Passed	b8ad370523037dba9f5430946e03c4f43d364944	View run #29733238320