Add filestore index mutex (#4886)

Author: c2thorn

mmv1/products/filestore/terraform.yaml

@@ -14,6 +14,7 @@
 --- !ruby/object:Provider::Terraform::Config
 overrides: !ruby/object:Overrides::ResourceOverrides
   Instance: !ruby/object:Overrides::Terraform::ResourceOverride
+    mutex: "filestore/{{project}}"
     error_retry_predicates: ["isNotFilestoreQuotaError"]
     timeouts: !ruby/object:Api::Timeouts
       insert_minutes: 6