Feature

Support importing templates from an upstream git repo that prompts for an update or auto upadtes when the upstream source of the template updates.

Motivation

I had this idea for a long time but was still determining how it would be implemented. Recently, I came across an example where Railway is doing something very similar.
https://blog.railway.app/p/updatable-starters

Possible Implementation

This can be implemented by authenticating a Coder GitHub OAuth app to monitor changes in the source code, trigger a new build, or prompt the user that an update is available.

1. User specifies the source repo and subdirectory of the template.
2. Coder imports and builds the template
3. Coder periodically or on every login checks for updates to the source repo and then prompts the user to update the template.
4. (Optionally) Asynchronously try to update the template and notify the users of the result of the update via a notification(we do not have them yet)

Thoughts are welcome: @ammario @bpmct @deansheather @kylecarbs