### Description of the change
Add config fallbacks for `session`, `cache` and `queue` including tests.
### Benefits
If users disable the default `redis-cluster` sub-chart dependency, this will configure the respective sections to use the Gitea defaults as listed in https://docs.gitea.com/next/administration/config-cheat-sheet.
### Possible drawbacks
Users will run on non-optimal settings for production without knowing their config.
### Applicable issues
- fixes#584#573#489#476#468#453
### 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`
- [x] Templating unittests are added
Co-authored-by: justusbunsi <sk.bunsenbrenner@gmail.com>
Co-authored-by: justusbunsi <justusbunsi@noreply.gitea.com>
Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/585
Reviewed-by: justusbunsi <justusbunsi@noreply.gitea.com>