Disable joins on Ci::Minutes::AdditionalPacks

What does this MR do?

Implements disable_joins on the Namespace -> Ci::Minutes::AdditionalPacks association to support the groupsharding effort to split the CI tables into their own DB.

This attribute is controlled by a feature flag that this MR also introduces, additional_packs_disable_joins

Related issue(s)

• Reduce the impact of future DB sharding work on recent CI minute provisioning work
• Update all relations to use disable_joins: that cross join many DBs

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.