fix(ci): improve workflows (#959)

🤖 Split up helm chart workflows

The following patch adapts the CI workflows. The worflows has been splitted into
dedicated parts. For example the `helm template` and `helm unittest` command is
now a seperate step to notice that a change affects the template mechanism but
not the unittest. This was priviously not possible, because both commands were
part of one step.

🤖 Changelog Issue

Additionally has the changelog workflow be improved. The shell commands has
been migrated to a dedicated file named `.gitea/scripts/changelog.sh`. This has
the advantage, that the shellcheck plugin of IDE's support developers by
developing such shell scripts. Furthermore, the used container image has been
replaced by the ubuntu:latest image of the act_runner. This make it more
comfortable in using `curl` or `jq`, because the complete set of features/flags
are
avialable instead of the previously used container image
`docker.io/thegeeklab/git-sv:2.0.5`. Final note to the shell script
`changelog.sh`, this can now be executed locally as well as on ARM-based
act_runners and helps to test the helm chart in own Gitea environments
beforehand.

🤖 Markdown linter

In addition, a new workflow for markdown files has now been introduced. This
checks the `README.md` file for links, ensures that it is properly formatted,
and verifies that the parameters match those in `values.yaml`. Here, too, the
commands have been outsourced to separate jobs so that more precise interaction
is possible in the event of an error.

⚠️ Warning

This patch also requires an adjustment in branch protection. There, the
workflows that must be successful before a merge must be redefined.

Reviewed-on: https://gitea.com/gitea/helm-gitea/pulls/959
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Markus Pesch <markus.pesch@cryptic.systems>
Co-committed-by: Markus Pesch <markus.pesch@cryptic.systems>

CONTRIBUTING.md

@@ -44,8 +44,7 @@ be used:
    `helm install --dependency-update gitea . -f values.yaml`.
 1. Gitea is now deployed in `minikube`.
    To access it, it's port needs to be forwarded first from `minikube` to localhost first via `kubectl --namespace
-default port-forward svc/gitea-http 3000:3000`.
-   Now Gitea is accessible at [http://localhost:3000](http://localhost:3000).
+default port-forward svc/gitea-http 3000:3000`. Now Gitea is accessible at [http://localhost:3000](http://localhost:3000).
 
 ### Unit tests