Make AWS Code Commit Repo Permissions Management more user friendly

[dennisknothetelus]

We use AWS Code Commit as one of our main code hosts, alongside various GitHub organizations.

Once we configured AWS Code Commit as code host, all those repos showed up as "Public", i.e. are visible to all our users. This is not intended. We would like to only have users AWS Code Commit access to be able to view those repos in Sourcegraph.

Using the Explicit Permissions API https://sourcegraph.com/docs/admin/permissions/api is extremely cumbersome to manage such permissions.

Please support both of the following ways to manage user permissions

1. It should be possible through the Sourcegraph Site Admin UI to easily configure manually the permissions for certain user groups (e.g. create a role "AWS Code Commit repos", grant that role access to all "AWS Code Commit" repos, then assign that role manually to all users who need that access. This should be supported for all costs hosts, and be possible to set manually regardless of any code host sync'ed permissions. The manual setting should overwrite any sync'ed permissions.

2. Please also support SSO and sync'ed permissions for AWS Code Commit (like it is supported for GitHub today)