Add protected tag deploy key support
Add support for `create_access_levels[].deploy_key_id` to `protected_tags.go`
Related API docs https://docs.gitlab.com/api/protected_tags/
## Implementation Guide
- Read the `CONTRIBUTING.md` guide for setting up your local development and fork the community clone of this project.
- In `protected_tags.go`, add `DeployKeyID` to the `TagAccessDescription` struct.
- Add `DeployKeyID` to the `TagsPermissionOptions` struct.
- Update the unit tests in `protected_tags_test.go` to include test cases with `DeployKeyID`.
- Could also create an integration test for this! See `gitlab_test/users_integration_test.go` as an example.
- Run `make reviewable` before raising an MR.
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