feature: Atlantis should support gitHub groups for approving polices along with individual users

[stark-tech25]

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Overview of the Issue

Currently Atlantis only supports individual users as owners to approve failed policies. Each user needs to be hardcoded in the atlantis.yaml
Having the option to use a GitHub team would extend this feature to all members of the group with out having to hard code each member in the config.

Atlantis server-side config file:

Repo atlantis.yaml file:

**Current Implementation:**
    repos:
    - id: github.test/test
      apply_requirements: []
      workflow: test
      allowed_overrides: []
      allow_custom_workflows: false
    policies:
      owners:
        users:
          - user1
          - user2
      policy_sets:
        - name: atlantis-conf-tests
          owners:
            users:
              - user1
              - user2
          path: /github_atlantis/policy
          source: local  

**Expected feature**
    repos:
    - id: github.test/test
      apply_requirements: []
      workflow: test
      allowed_overrides: []
      allow_custom_workflows: false
    policies:
      owners:
        team:
          - team1
      policy_sets:
        - name: atlantis-conf-tests
          owners:
            team:
              - team1
          path: /github_atlantis/policy
          source: local  

[guidor]

I think this was added in v0.24.0 #3086

[pippitt]

I think this was added in v0.24.0 #3086

Verified this does work with github using:

policies:
    owners:
      teams:
        - team1

Haven't tested on individual policies, but expect the same syntax looking at the code will work.
Didn't see reference to using teams in the docs.