Summary:

- Start `K8s.Conn.Auth.ProviderSupervisor`
- Start `K8s.Conn.Auth.ExecWorker` for kube context with auth exec
  configured. This respects expiration and will not give out known
  expired tokens.
- Start `K8s.Conn.Auth.ServiceAccountWorker` for connections started
  with `K8s.Conn.from_service_account/2`. This periodically refreshes
  the token.
- Add refresh timers with jitter on for all of those
- Start `K8s.Conn.Auth.CertificateWorker` for kube context where given a
  .pem file. Some cloud providers are giving very short duration certs.

Test Plan:

- Added test for exec parsing
- Added test for exec worker
- Added test for service account
- Added integration-ish test for service account worker refresh
- Changed test for certificate to ensure genserver
- Added test for certificate worker

`mix test`

Summary:
This adds on a registry and a standard name for many of the auth
providers. It allows for shared workers when the paths are the same and
for genserver to crash, get re-started and not have errors due to stale
pids.

Test Plan:
Tests were updated