chore: add GitHub automation for IAM and Admin Exp team

Created by: unknwon

Three parts of GitHub automation have been added for the IAM and Admin Exp team:

1. .github/teams.yml: Automatically label the PR with the label team/iam-admin-experience if the author is one of defined people.
2. .github/workflows/label-move.yml: Automatically add issues and PRs with the label team/iam-admin-experience to the IAM and Admin Exp GitHub project.
3. .github/workflows/label-notify.yml: Automatically tag @sourcegraph/iam-and-admin-experience team when an issue is labeled with team/iam-admin-experience
   • This could be a bit controversial, there will be times with some issue storm, we can change it to only individuals if we want. Let's start with it see how things go.

Test plan

Not code related.