Add mechanism for k8s charms/images to pull secrets from k8s secret stores

[Barry Price]

Secrets in charm config end up stored in plaintext on the Juju controller - ideally any given charm/image would be able to natively use Kubernetes secrets without exposing them to the controller or (potentially) in logs:

https://kubernetes.io/docs/concepts/configuration/secret/

[Pen Gale (pengale)]

We've got some work scheduled this cycle to plan for better modeled secrets across Juju clouds. Actual implementation would happen sometime in the 21.10 cycle (or later).

I linked this bug into the spec covering the work, so that we are sure to consider k8s native mechanisms when designing our secrets framework.

[Canonical Juju QA Bot (juju-qa-bot)]

This Medium-priority bug has not been updated in 60 days, so we're marking it Low importance. If you believe this is incorrect, please update the importance.

[Harry Pidcock (hpidcock)]

Adding wallyworld as I believe this feature is being worked on now.

[Vitaly Antonenko (anvial)]

This is already implemented in Juju 3.1 or later as the "Juju Secrets" feature.