Pass AuthContext to Python Mutator Functions / Create WorkspaceClient without additional config

[mniehoff]

Describe the issue

It would be really nice if one could use the WorkspaceClient in the Python Mutator functions by just creating it with WorkspaceClient, without passing any auth argument again. It should just reuse the AuthContext that is used for the cli (e.g. when calling databricks bundle deploy)

Configuration

Add a mutator function, call WorkspaceClient() in it, without arguments. It will fail with cannot configure default credentials, please check https://docs.databricks.com/en/dev-tools/auth.html#databricks-client-unified-authentication to configure credentials for your preferred authentication method. when running databricks bundle deploy

Expected Behavior

WorkspaceClient should be initiated with the Auth of the CLI call.

[varundeepsaini]

@andrewnester wanted to pick this up

was planning to

Pass auth env vars to the Python mutator subprocess by:

1. Getting auth.Env(b.Config.Workspace.Config()) in Apply()
2. Adding process.WithEnvs(authEnvs) to the process.Background() call in runPythonMutator()

Saw this approach in cmd/labs/project/entrypoint.go.

Any concerns before I raise a pr?