AlloyDB read poll support and various usability fixes (#3061)

* AlloyDB read poll support and various usability fixes

* Added support for read poll instances.
* Added support for public (outbound) IPs.
* Added new arguments: `machine_type`, `skip_await_major_version_upgrade`, and `subscription_type`.
* Added outputs for key cluster attributes, including ID and name.
* Improved input variable validations and simplified configurations.
* Fixed bug where AlloyDB user accounts always had null passwords.
* Resolved Terraform state drift issues for `network_config` and `psc_config`.
* Fixed `continuous_backup_config` always being implicitly or explicitly enabled.
* Fixed `automated_backup_policy` and `maintenance_update_policy`, which do not support non-zero minutes, seconds and nanos.
* Fixed various typos.
* Aligned the format of test examples.

* Fixed invalid condition: authorized external networks require enabled public IP, however enabled public IP can have empty authorized external networks

* Formatting

* Fix PSA block

---------

Co-authored-by: Julio Castillo <jccb@google.com>

tests/modules/alloydb/examples/simple.yaml

@@ -30,14 +30,13 @@ values:
     labels: null
     location: europe-west8
     maintenance_update_policy: []
-    network_config:
-    - allocated_ip_range: null
     project: test-alloydb
-    psc_config:
-    - psc_enabled: null
+    psc_config: []
     restore_backup_source: []
     restore_continuous_backup_source: []
     secondary_config: []
+    skip_await_major_version_upgrade: true
+    subscription_type: STANDARD
     timeouts: null
   module.alloydb.google_alloydb_instance.primary:
     annotations: null
@@ -49,9 +48,6 @@ values:
     labels: null
     machine_config:
     - cpu_count: 2
-    network_config:
-    - authorized_external_networks: []
-      enable_public_ip: false
     query_insights_config:
     - query_plans_per_minute: 5
       query_string_length: 1024