Add support for organization security managers

[jeremyhayes]

Resolves #1210

---

Behavior

Before the change?

Users cannot manage security manager teams for their organizations.

After the change?

Users CAN manage security manager teams for their organizations.

Template would look similar to:

resource "github_team" "some_team" {
  name        = "SomeTeam"
  description = "Some cool team"
}
resource "github_organization_security_manager" "some_team" {
  team_slug = github_team.some_team.slug
}

Other information

• n/a

---

Additional info

Pull request checklist

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Added the appropriate label for the given change

Does this introduce a breaking change?

Please see our docs on breaking changes to help!

• Yes (Please add the Type: Breaking change label)
• No

If Yes, what's the impact:

• N/A

Pull request type

Please add the corresponding label for change this PR introduces:

• Bugfix: Type: Bug
• Feature/model/API additions: Type: Feature
• Updates to docs or samples: Type: Documentation
• Dependencies/code cleanup: Type: Maintenance

---

[jeremyhayes]

Please add the corresponding label for change this PR introduces:

I think a maintainer will need to add the Type: Feature label.

[kfcampbell]

I've confirmed that acceptance tests are passing for me locally. Thank you for the contribution! I love the docs and testing updates.