[NocoDB] Pull NC_DB secret from Kubernetes in Helm Chart

### Please confirm that the feature request does ***not*** already exist - [x] I confirm there is no existing issue for this feature request. ### Use case 1) In most deployment patterns, database connection strings should not be stored in version control in plain text and instead should be pulled from a remote secrets store. 2) In Kubernetes this is often a Kubernetes Secret resource which can be updated by an external secrets library. 3) To enable this in Kubernetes the helm chart should be modied so that values.yaml file can point the deployment at a secret name and key reference to pull the NC_DB secret. ### Suggested solution I have created a fork which provides a basic working example of the described requirements and well as maintaining backwards compatability for a NC_DB string stored in values. Also in this fork is dynamic probe variables which can be removed if necessary for PR however does have use cases. https://github.com/PaulieNor/nocodb ### Additional context _N