…usable workflows

Adds 5 new reusable workflows to support standardized CI/CD across
cloudoperators repos (shoot-grafter, repo-guard, permission-manager,
cloudctl, greenhouse-extensions):

- shared-go-lint.yaml: golangci-lint + optional govulncheck
- shared-go-test.yaml: parameterized make test target + optional coverage upload
- shared-go-build.yaml: Go binary build + optional Docker multi-arch build/push
- shared-release.yaml: semver bump, Chart.yaml update, release PR + GitHub release + optional greenhouse-extensions dispatch
- shared-e2e.yaml: KinD-based e2e wrapping the existing workflows/e2e composite action

Closes #2086

Signed-off-by: I313226 <onur.yilmaz@sap.com>

…-test job

Signed-off-by: I313226 <onur.yilmaz@sap.com>

- Checkout default branch explicitly (ref: default_branch) so releases
  are never cut from a feature branch
- Use github.event.repository.default_branch instead of hard-coded 'main'
  for PR base and release --target, supporting non-main default branches
- Quote ${{ inputs.makefile-path }} in grep invocation
- Quote ${{ inputs.chart-path }} in both sed commands
- Create GitHub release targeting the default branch after fetching
  latest, so the tag points at the correct merged commit

Signed-off-by: I313226 <onur.yilmaz@sap.com>

- shared-go-test: drop go-version input, always use go-version-file from go.mod
- shared-release: add if condition to Update Makefile VERSION step (skip when makefile-path is empty)
- shared-release: split Chart.yaml update into two steps with separate bump-chart-app-version input
- shared-release: replace gh CLI release creation with actions/github-script@v7
- shared-release: replace dispatch-token with GitHub App token via actions/create-github-app-token@v3 and peter-evans/repository-dispatch@v4

Signed-off-by: I313226 <onur.yilmaz@sap.com>

…criptions

Signed-off-by: I313226 <onur.yilmaz@sap.com>

… inputs.remote-k8s-version

Signed-off-by: I313226 <onur.yilmaz@sap.com>

… is now truly optional

Signed-off-by: I313226 <onur.yilmaz@sap.com>

…r with ERROR:

- shared-go-lint: validate GOVULNCHECK_VERSION against semver/latest pattern
  before interpolating into go run command to prevent injection
- shared-release: prefix invalid bump type message with ERROR: for consistency
  with other validation failures in the workflow

Signed-off-by: I313226 <onur.yilmaz@sap.com>

…vulncheck step

- shared-release: change makefile-path default from "Makefile" to "" so
  chart-only callers don't need to override it to avoid the file-existence
  check failing on a non-existent Makefile
- shared-go-lint: add shell: bash to govulncheck step to ensure bash
  builtins and grep work correctly regardless of runner OS default shell

Signed-off-by: I313226 <onur.yilmaz@sap.com>

…; fix e2e output path

- shared-release: strip inline Makefile comments (e.g. '# comment') from
  the VERSION value before semver validation to avoid false parse failures
- shared-release: preserve the original assignment operator (?=, :=, =)
  when rewriting VERSION in the Makefile instead of normalising to '='
- e2e/action: output E2E_REPORT_PATH (.json report) instead of
  CONTROLLER_LOGS_PATH (.txt logs) to match the declared output description

Signed-off-by: I313226 <onur.yilmaz@sap.com>