fix(storage): rename Publisher and Subscription admin clients (#3349)

The admin clients should be renamed to match their function. This is consistent with the Java and Go client libraries, though theirs are named TopicAdminClient and SubscriptionAdminClient. Since these types are within a client module, we do not use the suffix since its repetitive.

For #3011 and for #3010

Author: suzmue

src/pubsub/src/generated/gapic/.sidekick.toml

@@ -14,7 +14,7 @@
 
 [general]
 specification-source = 'google/pubsub/v1'
-service-config = 'google/pubsub/v1/pubsub_v1.yaml'
+service-config       = 'google/pubsub/v1/pubsub_v1.yaml'
 
 [source]
 included-ids = """\
@@ -45,3 +45,4 @@ included-ids = """\
 copyright-year        = '2025'
 template-override     = 'templates/http-client'
 package-name-override = 'google-cloud-pubsub'
+name-overrides        = '.google.pubsub.v1.Publisher=TopicAdmin,.google.pubsub.v1.Subscriber=SubscriptionAdmin'