Increase the default complexity of Cloud SQL DB passwords (#2886)

* Increase the default complexity of DB passwords in order to meet password_validation_policy.default_complexity

* Use password_validation_policy.min_length if provided

* Explicitly generate a root_password if not provided

* Use object (password, random_password) for root_password config

* Make root_password non-nullable, and add validation against specifying both a password and `random_password`.
Fix test for stronger password generation.

* Add example for root_password and password_validation_policy

* Rerun tfdoc.py

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

tests/modules/cloudsql_instance/examples/custom.yaml

@@ -49,10 +49,10 @@ values:
     keepers: null
     length: 16
     lower: true
-    min_lower: 0
-    min_numeric: 0
-    min_special: 0
-    min_upper: 0
+    min_lower: 1
+    min_numeric: 1
+    min_special: 1
+    min_upper: 1
     number: true
     numeric: true
     override_special: null