chore: Implements tags and labels as MapAttribute in advanced_cluster schema v2

[lantoli]

Description

Implements tags and labels as MapAttribute in advanced_cluster schema v2.

Link to any related issue(s): CLOUDP-295198

Type of change:

• Bug fix (non-breaking change which fixes an issue). Please, add the "bug" label to the PR.
• New feature (non-breaking change which adds functionality). Please, add the "enhancement" label to the PR. A migration guide must be created or updated if the new feature will go in a major version.
• Breaking change (fix or feature that would cause existing functionality to not work as expected). Please, add the "breaking change" label to the PR. A migration guide must be created or updated.
• This change requires a documentation update
• Documentation fix/enhancement

Required Checklist:

• I have signed the MongoDB CLA
• I have read the contributing guides
• I have checked that this change does not generate any credentials and that they are NOT accidentally logged anywhere.
• I have added tests that prove my fix is effective or that my feature works per HashiCorp requirements
• I have added any necessary documentation (if appropriate)
• I have run make fmt and formatted my code
• If changes include deprecations or removals I have added appropriate changelog entries.
• If changes include removal or addition of 3rd party GitHub actions, I updated our internal document. Reach out to the APIx Integration slack channel to get access to the internal document.

Further comments

[lantoli]

@EspenAlbert can you confirm this change is ok for container_id ?

[lantoli]

@EspenAlbert do we need to keep this logic to send an empty value instead of null value, or it's ok with the previous change in ToTFMapOfString to treat empty maps as null?

as in mocked tests, with this change we don't send the value to Atlas instead of [] being done now:

   - "labels": [],
          "mongoDBMajorVersion": "8.0",
        @@ -61,4 +60,3 @@
           }
        - ],
        - "tags": []
        + ]
         }