Ignore unrelated helm files from bundling (#385)

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### Description of the change
Exluding non helm chart related files from release artifact

### Benefits
Smaller release artifacts

### Possible drawbacks
Exluded files not visible any within the artifact

### Applicable issues
None

### Additional information
None

### ⚠ BREAKING
None

### Checklist

<!-- [Place an '[X]' (no spaces) in all applicable fields. Please remove unrelated fields.] -->

- [x] Parameters are documented in the `values.yaml` and added to the `README.md` using [readme-generator-for-helm](https://github.com/bitnami-labs/readme-generator-for-helm)
- [x] Breaking changes are documented in the `README.md`

Co-authored-by: Julian Schlarb <js@project-deadline.com>
Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/385
Reviewed-by: justusbunsi <justusbunsi@noreply.gitea.io>
Reviewed-by: pat-s <pat-s@noreply.gitea.io>
Co-authored-by: JSchlarb <jschlarb@noreply.gitea.io>
Co-committed-by: JSchlarb <jschlarb@noreply.gitea.io>

.helmignore

@@ -25,3 +25,8 @@ node_modules/
 package.json
 package-lock.json
 .gitea/
+Makefile
+.markdownlintignore
+.markdownlint.yaml
+.drone.yml
+CONTRIBUTING.md