service_account_config for Cloud Run v2

Additional changes:
* align vpc-connector interface to Cloud Functions
* split managed and unmanaged resources into separate files, this makes
  easier to introduce further changes
* add support for contexts
* move `vpc_connector` variable to variables.tf for Cloud Functions
* remove `create` from `vpc_connector` in Cloud Functions as it was
  sharing the meaning with `vpc_connector_create`

tests/modules/cloud_function_v2/context-subnet-project.tfvars

@@ -43,8 +43,7 @@ service_account_config = {
   ]
 }
 vpc_connector = {
-  create = true
-  name   = "connector_name"
+  name = "connector_name"
 }
 vpc_connector_create = {
   instances = {

tests/modules/cloud_function_v2/context-subnet.tfvars

@@ -43,8 +43,7 @@ service_account_config = {
   ]
 }
 vpc_connector = {
-  create = true
-  name   = "connector_name"
+  name = "connector_name"
 }
 vpc_connector_create = {
   instances = {

tests/modules/cloud_function_v2/context.tfvars

@@ -43,8 +43,7 @@ service_account_config = {
   ]
 }
 vpc_connector = {
-  create = true
-  name   = "connector_name"
+  name = "connector_name"
 }
 vpc_connector_create = {
   ip_cidr_range = "$cidr_ranges:test"