Add flag to disable partition check on startup

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/228857

config/initializers/postgres_partitioning.rb

@@ -4,7 +4,7 @@
 # (even with eager loading disabled).
 
 begin
-  Gitlab::Database::Partitioning::PartitionCreator.new.create_partitions
+  Gitlab::Database::Partitioning::PartitionCreator.new.create_partitions unless ENV['DISABLE_POSTGRES_PARTITION_CREATION_ON_STARTUP']
 rescue ActiveRecord::ActiveRecordError, PG::Error
   # ignore - happens when Rake tasks yet have to create a database, e.g. for testing
 end