AzureManagedCluster E2E: AdditionalTags CRUD tests

[dtzar]

/kind feature
/area managedclusters

Describe the solution you'd like
Create new AzureManagedCluster E2E: AdditionalTags CRUD tests

[jackfrancis]

Deliverables:

1. Test "create" additionalTags against both system and user node pool.
2. Test "update" additionalTags against pools, and against AzureManagedControlPlane as well
3. Test "delete" additionalTags against pools and AzureManagedControlPlane

@CecileRobertMichon I assume #3 is fine for AzureManagedControlPlane?, in other words, the tags that we define in our test template "buildProvenance", "creationTimestamp", and "jobName") aren't required in any way and we can delete them in an E2E scenario?

[jackfrancis]

/assign @nojnhuh

[jackfrancis]

In terms of "deleting all tags", the aks CLI docs suggest you do that via an empty string value:

--tags                : Space-separated tags: key[=value] [key[=value] ...]. Use
                      '' to clear existing tags.