Resolve "Migrate merge_request_metrics.id to bigint"

What does this MR do and why?

Prepare conversion of merge_request_metrics.id to bigint.

Up:

main: == 20230127093353 InitializeConversionOfMergeRequestMetricsToBigint: migrating
main: -- table_exists?(:merge_request_metrics)
main:    -> 0.0754s
main: -- column_exists?(:merge_request_metrics, :id)
main:    -> 0.0029s
main: -- column_exists?(:merge_request_metrics, :id)
main:    -> 0.0012s
main: -- transaction_open?()
main:    -> 0.0000s
main: -- columns(:merge_request_metrics)
main:    -> 0.0015s
main: -- add_column(:merge_request_metrics, "id_convert_to_bigint", :bigint, {:default=>0, :null=>false})
main:    -> 0.0029s
main: == 20230127093353 InitializeConversionOfMergeRequestMetricsToBigint: migrated (0.1127s)

main: == 20230127101834 BackfillMergeRequestMetricsForBigintConversion: migrating ===
main: -- table_exists?(:merge_request_metrics)
main:    -> 0.0039s
main: -- column_exists?(:merge_request_metrics, :id)
main:    -> 0.0023s
main: -- column_exists?(:merge_request_metrics, :id)
main:    -> 0.0010s
main: -- column_exists?(:merge_request_metrics, "id_convert_to_bigint")
main:    -> 0.0009s
main: == 20230127101834 BackfillMergeRequestMetricsForBigintConversion: migrated (0.0646s)

ci: == 20230127101834 BackfillMergeRequestMetricsForBigintConversion: migrating ===
ci: -- The migration is skipped since it modifies the schemas: [:gitlab_main].
ci: -- This database can only apply migrations in one of the following schemas: [:gitlab_ci, :gitlab_shared, :gitlab_internal].
ci: == 20230127101834 BackfillMergeRequestMetricsForBigintConversion: migrated (0.0045s)

Down:

main: == 20230127101834 BackfillMergeRequestMetricsForBigintConversion: reverting ===
main: -- execute("DELETE FROM batched_background_migrations WHERE job_class_name = 'CopyColumnUsingBackgroundMigrationJob' AND table_name = 'merge_request_metrics' AND column_name = 'id' AND job_arguments = '[[\"id\"],[\"id_convert_to_bigint\"]]'")
main:    -> 0.0063s
main: == 20230127101834 BackfillMergeRequestMetricsForBigintConversion: reverted (0.0077s)

main: == 20230127093353 InitializeConversionOfMergeRequestMetricsToBigint: reverting
main: -- remove_column(:merge_request_metrics, "id_convert_to_bigint")
main:    -> 0.0008s
main: == 20230127093353 InitializeConversionOfMergeRequestMetricsToBigint: reverted (0.0043s)

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Related to #389516 (closed)