[feature]: File-based provisioning / environmental variables for authentication

Is there an existing issue for this?

• I have searched the existing issues

Summary

Currently, it seems like the only way to configure auth is to go to /god-mode/authentication and click through authentication options. For the sake of enabling best-practice ops and automation, Plane should provide both file-based provisioning and environmental variables to configure auth (this likely applies to other areas too).

For reference on the kind of thing we'd like to see: see Grafana's provisioning documentation: https://grafana.com/docs/grafana/latest/administration/provisioning/

Why should this be worked on?

Without this, we are unable to reliably automate, version, and script out our configuration management, especially across environments, which leaves us with manual, error-prone processes that do not scale.