Adds support for `advanced_datapath_observability_config` to the `gke-cluster-autopilot` module, matching the standard cluster module implementation.
Closes#3936
TAG=agy
CONV=9d4485ab-0fae-4f3d-a6e1-bbb6320d7c46
* gke-cluster-autopilot: add support for network tags
* gke-cluster-autopilot: add validation for network tags
* gke-cluster-autopilot: expand README and fix some typos
* gke-cluster-autopilot: fix Cloud DNS section in README
Removed a reference to Standard clusters and updated the section to include a warning because the new versions of Autopilot clusters can only use Cloud DNS and it is pre-configured by default so the example in the README does not apply to them.
* gke-cluster-autopilot: cosmetic fixes in README
* gke-cluster-autopilot: rollback validation on network tags var
* gke-cluster-autopilot: rollback docs string update for network tags var
* gke-cluster-autopilot: rollback some updates to README
* gke-cluster-autopilot: remove dead code
* gke-cluster-autopilot: add a tftest for network tags
* gke-cluster-autopilot: fix a tftest
