Update each property of Memorystore instances in a separate request

[modular-magician]

Fixes hashicorp/terraform-provider-google#20101

This PR updates the Memorystore Instance definition to submit updates for multiple properties in multiple PATCH requests, one per property.

The Memorystore API allows updating only one instance field per PATCH request, but the provider was sending all changed fields in a single request (e.g., updateMask=replicaCount,engineConfigs), causing updates to multiple fields to fail with:

Error: Error updating Cluster "projects/foobar/locations/us-west2/clusters/primary": googleapi: Error 400: exactly 1 update_mask field must be specified per update request
Details:
[
  {
    "@type": "type.googleapis.com/google.rpc.BadRequest",
    "fieldViolations": [
      {
        "field": "update_mask"
      }
    ]
  }
]

  with module.app.google_redis_cluster.primary,
  on ../../modules/app/redis.tf line 29, in resource "google_redis_cluster" "primary":
  29: resource "google_redis_cluster" "primary" {

Each of the 11 mutable non-label properties now specifies update_id, update_verb, and update_url (with a single-field updateMask query parameter).

I left labels in the main update path because it seems KeyValueLabels is handled specially as part of the provider's built-in handling for merging provider-level default labels with resource-level labels (via effective_labels and terraform_labels). As the sole remaining field in the main update body, I think that should work, but let me know if I misinterpreted the behavior here.

I also added a test to cover a multi-property update and confirmed it now works on a test GCP project.

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memorystore: fixed an issue preventing updating multiple properties at once for `google_redis_cluster`

Derived from GoogleCloudPlatform/magic-modules#17166