Initialize conversion of ci_builds_runner_session.build_id to bigint

What does this MR do?

This MR starts conversion of ci_builds_runner_session.build_id to bigint.

See #328444 (closed).

Database migrations

Up

$ bundle exec rails db:migrate
== 20210427084924 InitializeConversionOfCiBuildsRunnerSessionToBigint: migrating 
-- table_exists?(:ci_builds_runner_session)
   -> 0.0019s
-- column_exists?(:ci_builds_runner_session, :id)
   -> 0.0020s
-- column_exists?(:ci_builds_runner_session, :build_id)
   -> 0.0013s
-- columns(:ci_builds_runner_session)
   -> 0.0014s
-- add_column(:ci_builds_runner_session, "build_id_convert_to_bigint", :bigint, {:default=>0, :null=>false})
   -> 0.0051s
== 20210427084924 InitializeConversionOfCiBuildsRunnerSessionToBigint: migrated (0.0432s) 

== 20210427085020 BackfillCiBuildsRunnerSessionForBigintConversion: migrating =
-- table_exists?(:ci_builds_runner_session)
   -> 0.0016s
-- column_exists?(:ci_builds_runner_session, :id)
   -> 0.0012s
-- column_exists?(:ci_builds_runner_session, :build_id)
   -> 0.0012s
-- column_exists?(:ci_builds_runner_session, "build_id_convert_to_bigint")
   -> 0.0013s
unknown OID 28: failed to recognize type of 'relfrozenxid'. It will be treated as String.
unknown OID 1034: failed to recognize type of 'relacl'. It will be treated as String.
unknown OID 194: failed to recognize type of 'relpartbound'. It will be treated as String.
== 20210427085020 BackfillCiBuildsRunnerSessionForBigintConversion: migrated (0.0660s)

Down

$ bundle exec rails db:migrate:down VERSION=20210427085020
== 20210427085020 BackfillCiBuildsRunnerSessionForBigintConversion: reverting =
-- execute("DELETE FROM batched_background_migrations WHERE job_class_name = 'CopyColumnUsingBackgroundMigrationJob' AND table_name = 'ci_builds_runner_session' AND column_name = 'id' AND job_arguments = '[[\"build_id\"],[\"build_id_convert_to_bigint\"]]'")
   -> 0.0041s
== 20210427085020 BackfillCiBuildsRunnerSessionForBigintConversion: reverted (0.0044s) 


$ bundle exec rails db:migrate:down VERSION=20210427084924
== 20210427084924 InitializeConversionOfCiBuildsRunnerSessionToBigint: reverting 
-- remove_column(:ci_builds_runner_session, "build_id_convert_to_bigint")
   -> 0.0011s
== 20210427084924 InitializeConversionOfCiBuildsRunnerSessionToBigint: reverted (0.0048s) 

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because _____.
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #328444 (closed)