Remove pipeline foreign keys from package tables

🌻 What does this MR do and why?

In the effort to separate the ci_* database, we are removing all foreign keys that between ci_* tables and non ci_* tables. #338861 (closed) focuses on these efforts as related to the package stage.

In this MR we remove two foreign keys from packages_build_infos and packages_package_file_build_infos. We add a dependent: :nullify constraint to the Ci::Pipeline to preserve the behavior of the foreign keys being deleted.

:disk Database

🛫 Up migrations:

== 20210917153645 RemovePipelineFkFromPackagesBuildInfos: migrating ===========
-- transaction_open?()
   -> 0.0000s
-- foreign_keys(:packages_build_infos)
   -> 0.0060s
-- remove_foreign_key(:packages_build_infos, :ci_pipelines)
   -> 0.0078s
== 20210917153645 RemovePipelineFkFromPackagesBuildInfos: migrated (0.0500s) ==

== 20210917153905 RemovePipelineFkFromPackagesPackageFileBuildInfos: migrating 
-- transaction_open?()
   -> 0.0000s
-- foreign_keys(:packages_package_file_build_infos)
   -> 0.0031s
-- remove_foreign_key(:packages_package_file_build_infos, :ci_pipelines)
   -> 0.0054s
== 20210917153905 RemovePipelineFkFromPackagesPackageFileBuildInfos: migrated (0.0156s) 

🛬 Down migrations:

== 20210917153905 RemovePipelineFkFromPackagesPackageFileBuildInfos: reverting 
-- transaction_open?()
   -> 0.0000s
-- foreign_keys(:packages_package_file_build_infos)
   -> 0.0057s
-- transaction_open?()
   -> 0.0000s
-- execute("ALTER TABLE packages_package_file_build_infos\nADD CONSTRAINT fk_3e3f630188\nFOREIGN KEY (pipeline_id)\nREFERENCES ci_pipelines (id)\nON DELETE SET NULL\nNOT VALID;\n")
   -> 0.0026s
-- execute("SET statement_timeout TO 0")
   -> 0.0010s
-- execute("ALTER TABLE packages_package_file_build_infos VALIDATE CONSTRAINT fk_3e3f630188;")
   -> 0.0070s
-- execute("RESET statement_timeout")
   -> 0.0007s
== 20210917153905 RemovePipelineFkFromPackagesPackageFileBuildInfos: reverted (0.0502s) 

== 20210917153645 RemovePipelineFkFromPackagesBuildInfos: reverting ===========
-- transaction_open?()
   -> 0.0000s
-- foreign_keys(:packages_build_infos)
   -> 0.0030s
-- transaction_open?()
   -> 0.0000s
-- execute("ALTER TABLE packages_build_infos\nADD CONSTRAINT fk_17a9a0dffc\nFOREIGN KEY (pipeline_id)\nREFERENCES ci_pipelines (id)\nON DELETE SET NULL\nNOT VALID;\n")
   -> 0.0013s
-- execute("ALTER TABLE packages_build_infos VALIDATE CONSTRAINT fk_17a9a0dffc;")
   -> 0.0023s
== 20210917153645 RemovePipelineFkFromPackagesBuildInfos: reverted (0.0119s) ==

🎞 Screenshots or screen recordings

See section below (these commands are directly from my rails console).

✏ How to set up and validate locally

1. Run the migrations

2. Create a package build info object:

   Packages::BuildInfo.create(package: Packages::Package.first, pipeline: Ci::Pipeline.first)

3. Find the Pipeline from the build info and destroy it:

   Packages::BuildInfo.first
   => #<Packages::BuildInfo:0x00007fd3c9f286f0 id: 4, package_id: 1, pipeline_id: 1>
   Ci::Pipeline.find(1).destroy

4. The build info should now have a nil pipeline_id:

   Packages::BuildInfo.first
   => #<Packages::BuildInfo:0x00007fd36f16dec0 id: 4, package_id: 1, pipeline_id: nil>

5. Repeat for package file build infos:

   [59] pry(main)> Packages::PackageFileBuildInfo.create(package_file: Packages::PackageFile.first, pipeline: Ci::Pipeline.first)
   => #<Packages::PackageFileBuildInfo:0x00007fd36eca68b0 id: 4, package_file_id: 4, pipeline_id: 2>
   [60] pry(main)> Ci::Pipeline.find(2).destroy
   ...
   [62] pry(main)> Packages::PackageFileBuildInfo.last
   => #<Packages::PackageFileBuildInfo:0x00007fd33ffaee10 id: 4, package_file_id: 4, pipeline_id: nil>

🐧 MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #338861 (closed)