Integrations: support self-hosted providers from gkdev

[d13]

The goal is not to just convert over to GKdev like our other providers. We need to continue support of multiple instances of self-hosted and GKdev only supports one instance.

High level changes:

• Send users to GKdev to connect to self-hosted GitHub or GitLab
• Existing self-hosted integations (GitHub or GitLab) on GKdev, bring those into our system, but still support our custom self-hosted auth
• Once we have the info, we need to register a custom provider
• The code where this happens in remoteProviders.ts
• Essentially, we can just take the list of custom remotes and add another custom entry from the GKdev data, at runtime. We don't want to update their settings.json (though it might be an easy path for initial testing).

Potential gotchas:

• During development, if GKdev doesn't provide the correct data, let's just temporarily stub the data in while we wait for GKDS/GKdev to provide the info (aka URL)