Make agent_pool_id optional in resource azuredevops_agent_queue

[BHoggs]

All Submissions:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.
• My code follows the code style of this project.
• I ran lint checks locally prior to submission.
• Have you checked to ensure there aren't other open PRs for the same update/change?

What about the current behavior has changed?

Adds the attribute name to azuredevops_agent_queue, and make it mutually exclusive with the agent_pool_id attribute.

The API does not require a Pool ID to be specified when creating an Agent Queue, alternatively only a name needs to be specified.
In this scenario, the pool gets automatically created without explicitly requesting it. This is useful for creating agent pools at the project-level without needing org-level permissions to create pools.

Issue Number: #456

Does this introduce a change to go.mod, go.sum or vendor/?

• Yes
• No

Does this introduce a breaking change?

• Yes
• No

Other information

This is my first attempt at a PR for a terraform module and I'm pretty new at Go, so please let me know if I should have done anything differently!

[BHoggs]

@microsoft-github-policy-service agree company="Computer Concepts Limited"

[BHoggs]

@xuzhang3 Anything missing or need to be changed for this to get merged? Keen to get this across the line to unblock something on our end. :)

[xuzhang3]

=== RUN   TestAccResourceAgentQueue_CreateAndUpdate
=== PAUSE TestAccResourceAgentQueue_CreateAndUpdate
=== CONT  TestAccResourceAgentQueue_CreateAndUpdate
--- PASS: TestAccResourceAgentQueue_CreateAndUpdate (55.28s)
PASS
ok      github.com/microsoft/terraform-provider-azuredevops/azuredevops/internal/acceptancetests        55.665s

[xuzhang3]

@BHoggs LGTM