Prompt users to authenticate external_auth on workspace update

[matifali]

If a new external_auth is added to the template, there should be a way to prompt the user to authenticate.
Slack Message

Note

A new external authentication can be added directly as well as through a module to an existing template.

Workaround

Tip

Go to https://coder.eaxmple.com/settings/external-auth and authenticate/re-authenticate with the external provider manually.

[matifali]

I am promoting it as a bug as it breaks one of the core workflows.
For auto starts when updates are mandatory, we should hold updating such workspaces and show a banner to the user in SSH sessions and UI about authenticating with the newly added external authentication when they connect to their workspaces.

[matifali]

This is also valid if the current token is expired.

[BrunoQuaresma]

This would require the BE to return this info somewhere, probably in the workspace or template payload. cc.: @mtojek

[mtojek]

@BrunoQuaresma Which information do you mean exactly? Can you suggest a JSON snippet, so we can drill it down?