Allow skip fetch members/repos for github_team data source

[jeffgran]

Since a lot of resources (graphql-based ones) now require us to use the team's Node ID instead of just the slug, we often have to use data sources just to look up the ID of the team. However, this is an extreme performance drag because some teams have dozens or hundreds of repositories and members to look up page-wise. We don't need any of that, all we need is the Node ID. So we'd like an option to disable those lookups to speed this up and reduce the chance of rate limiting issues.