Allow defining the config with the backend in a Secret instead of a ConfigMap

[froblesmartin]

Is your feature request related to a problem? Please describe.

Currently the suggested (and only way?) way to configure a Pyroscope backend in the Helm chart is by writing the credentials in plain text in the values.

Describe the solution you'd like

Allow defining the config with the backend in a Secret instead of a ConfigMap.

This could be done with a key in the values.yaml to switch between ConfigMap to defining a Secret to mount in the pods. Then the secret can be provisioned externally with each one's method.

Describe alternatives you've considered

Using the provider default logic. In my case with GCP GCS, with the JSON file where the environment variable GOOGLE_APPLICATION_CREDENTIALS defines or the well-known $HOME/.config/gcloud/application_default_credentials.json, or with the metadata server and the flag -storage.gcs.service-account.