feat: add gke_backup_agent_config arg

[DrFaust92]

Closes #1257

[bharathkkb]

Thanks for the PR @DrFaust92

[comment-bot-dev]

@DrFaust92
Thanks for the PR! 🚀
✅ Lint checks have passed.

[wyardley]

Is it expected that it takes a really long time to apply the change (like 20-30m), even though the backup config is already disabled?

Similar behavior to mine, btw (#1332)

~ resource "google_container_cluster" "primary" {
        id                          = "projects/xxxx"
        name                        = "xx"
        # (28 unchanged attributes hidden)

      ~ addons_config {

          + gke_backup_agent_config {
              + enabled = false
            }

            # (9 unchanged blocks hidden)
        }

        # (20 unchanged blocks hidden)
    }