Convert primary keys to bigint for ci_pipeline_variables

It looks like it's more complex/impossible without downtime to change a primary key after the table is partitioned since we can't use our current workflow on partitioned tables:

PG::FeatureNotSupported: ERROR:  ALTER TABLE / ADD CONSTRAINT USING INDEX is not supported on partitioned tables

The primary key for ci_pipeline_variables is still using integer type and we need to have it converted to bigint before starting to partition that table.

This will take 4 releases(milestones) to be completed.

Process

Following the process outlined here, we must:

Step	MR	Workflow Status	Milestone
Initialize the conversion	!118878 (merged)	workflowcomplete	%16.0
Swap the columns	- Async Index !120946 (merged) - Sync Index !120950 (merged) - Swap the columns !120823 (merged)	workflowcomplete workflowcomplete workflowcomplete	%16.1
Remove the trigger and old integer columns	!124026 (merged)	workflowcomplete	%16.2
Remove ignore rules	!125187 (merged)	workflowcomplete	%16.3