API endpoints to retrieve integration credentials

[Pwuts]

• Part of Implement front-to-back GitHub OAuth support on blocks #8002

We need the following endpoints:

• GET /integrations/{provider}/credentials - list all credentials for a provider, without secrets (metadata only)
• GET /integrations/{provider}/credentials/{cred_id} - retrieve a set of credentials (including secrets)

OAuth email access

1. Google, need scopes: email, (and likely) openid, profile
   Accessed at: https://www.googleapis.com/oauth2/v2/userinfo
   Useful Stackoverflow discussion
2. GitHub, scopes: user:email
   API docs
3. Notion; scopes are set in Capabilities
   Email is returned with access token response object at: owner.person.email for non-bot users