ci: create upcoming changelog via git-sv (#794)

https://github.com/thegeeklab/git-sv

- Creates a changelog from conventional commits
- Updates the changelog in an static issue (creates the issue if missing)
- Only runs after a new commit was merged into `main`
- Automatically determines the next version based on conv commits logic
- Follows up on #788

---

The logic can also be used to create the release notes on `tag` events and the subsequent Gitea release. Didn't wanted to add all at once, though.

Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/794
Reviewed-by: justusbunsi <justusbunsi@noreply.gitea.com>
Co-authored-by: pat-s <patrick.schratz@gmail.com>
Co-committed-by: pat-s <patrick.schratz@gmail.com>

.helmignore

@@ -37,3 +37,5 @@ unittests/
 .yamllint
 CODEOWNERS
 renovate.json5
+.commitlintrc.json
+.gitsv/