[US]: Create a consistent Helm Chart for Moodle

As a **Developer**, I want to have
- [x] a working helm charts for moodle `moodle` inside the charts folder
- [ ] a conditional dependency to bitnami's moodle's helm chart
- [x] a conditional dependency to bitnami's mariadb's helm chart
- [x] a conditional dependency to bitnami's postgresql's helm chart
- [x] a conditional dependency to bitnami's cloudnative pg's helm chart
- [x] a validator to ensure that all databases cannot be present at the same time
- [x] a default configuration for using external databases if required
- [ ] a go-function (helm) to ensure external secret configurations for each database
- [ ] a conditional dependency to maildev's helm chart (we'll create if there's none)
- [ ] a conditional dependency to postfix's helm chart
- [ ] a conditional dependency to minio's helm chart
- [ ] a `values.yaml` for each working environment (`local` => values-local.yaml, `dev` or `demo`, `prod` or staging)
- [ ] a test for services without tests
- [ ] a health check for services without health checks

so as to deploy a secure **Moodle** in one go using the `helm upgrade -i` command.