Swap packages_build_infos pipeline_id to bigint

What does this MR do and why?

As a part of migrating ci_pipeline-referencing columns to bigint, we need to create indexes for packages_build_infos.pipeline_id_convert_to_bigint.

This MR schedules the indexes to be created asynchronously on gitlab.com, a follow-up MR will be created for self-managed instances.

Required Stop?

16.11 is already being set as a required stop, which based on this comment, enables us to merge the finalization MRs as soon as the next release (or when it's done on Gitlab.com)

MR 3/8

Related to #454420 (closed)

db/post_migrate/20240416103210_prepare_async_indexes_for_packages_build_infos_pipeline_id_convert_to_bigint.rb

@@ -10,12 +10,12 @@ class PrepareAsyncIndexesForPackagesBuildInfosPipelineIdConvertToBigint < Gitlab
   COMPOSITE_INDEX_COLUMNS = [:package_id, :pipeline_id_convert_to_bigint, :id]
 
   def up
-    prepare_async_index TABLE_NAME, COLUMN_NAME, unique: true, name: INDEX_NAME
-    prepare_async_index TABLE_NAME, COMPOSITE_INDEX_COLUMNS, unique: true, name: COMPOSITE_INDEX_NAME
+    prepare_async_index TABLE_NAME, COLUMN_NAME, name: INDEX_NAME
+    prepare_async_index TABLE_NAME, COMPOSITE_INDEX_COLUMNS, name: COMPOSITE_INDEX_NAME
   end
 
   def down
-    unprepare_async_index TABLE_NAME, COLUMN_NAME, unique: true, name: INDEX_NAME
-    unprepare_async_index TABLE_NAME, COMPOSITE_INDEX_COLUMNS, unique: true, name: COMPOSITE_INDEX_NAME
+    unprepare_async_index TABLE_NAME, COLUMN_NAME, name: INDEX_NAME
+    unprepare_async_index TABLE_NAME, COMPOSITE_INDEX_COLUMNS, name: COMPOSITE_INDEX_NAME
   end
 end