Add max_seats_used_changed_at index

What does this MR do and why?

Issue: #358080 (closed)

This adds an index on column max_seats_used_changed_at in gitlab_subscriptions. We will be using this column in later MRs to find all subscriptions that have had max seats used changed on a daily basis.

Up

main: == 20221102225800 AddMaxSeatsUsedChangedAtIndexToGitlabSubscriptions: migrating
main: -- transaction_open?()
main:    -> 0.0000s
main: -- index_exists?(:gitlab_subscriptions, [:max_seats_used_changed_at, :namespace_id], {:name=>"index_gitlab_subscriptions_on_max_seats_used_changed_at", :algorithm=>:concurrently})
main:    -> 0.0044s
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0001s
main: -- add_index(:gitlab_subscriptions, [:max_seats_used_changed_at, :namespace_id], {:name=>"index_gitlab_subscriptions_on_max_seats_used_changed_at", :algorithm=>:concurrently})
main:    -> 0.0017s
main: -- execute("RESET statement_timeout")
main:    -> 0.0002s
main: == 20221102225800 AddMaxSeatsUsedChangedAtIndexToGitlabSubscriptions: migrated (0.0108s)

ci: == 20221102225800 AddMaxSeatsUsedChangedAtIndexToGitlabSubscriptions: migrating
ci: -- transaction_open?()
ci:    -> 0.0000s
ci: -- index_exists?(:gitlab_subscriptions, [:max_seats_used_changed_at, :namespace_id], {:name=>"index_gitlab_subscriptions_on_max_seats_used_changed_at", :algorithm=>:concurrently})
ci:    -> 0.0033s
ci: -- execute("SET statement_timeout TO 0")
ci:    -> 0.0001s
ci: -- add_index(:gitlab_subscriptions, [:max_seats_used_changed_at, :namespace_id], {:name=>"index_gitlab_subscriptions_on_max_seats_used_changed_at", :algorithm=>:concurrently})
ci:    -> 0.0019s
ci: -- execute("RESET statement_timeout")
ci:    -> 0.0007s
ci: == 20221102225800 AddMaxSeatsUsedChangedAtIndexToGitlabSubscriptions: migrated (0.0086s)

Down

main: == 20221102225800 AddMaxSeatsUsedChangedAtIndexToGitlabSubscriptions: reverting
main: -- transaction_open?()
main:    -> 0.0000s
main: -- indexes(:gitlab_subscriptions)
main:    -> 0.0042s
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0001s
main: -- remove_index(:gitlab_subscriptions, {:algorithm=>:concurrently, :name=>"index_gitlab_subscriptions_on_max_seats_used_changed_at"})
main:    -> 0.0011s
main: -- execute("RESET statement_timeout")
main:    -> 0.0001s
main: == 20221102225800 AddMaxSeatsUsedChangedAtIndexToGitlabSubscriptions: reverted (0.0093s)

ci: == 20221102225800 AddMaxSeatsUsedChangedAtIndexToGitlabSubscriptions: reverting
ci: -- transaction_open?()
ci:    -> 0.0000s
ci: -- indexes(:gitlab_subscriptions)
ci:    -> 0.0035s
ci: -- execute("SET statement_timeout TO 0")
ci:    -> 0.0001s
ci: -- remove_index(:gitlab_subscriptions, {:algorithm=>:concurrently, :name=>"index_gitlab_subscriptions_on_max_seats_used_changed_at"})
ci:    -> 0.0017s
ci: -- execute("RESET statement_timeout")
ci:    -> 0.0001s
ci: == 20221102225800 AddMaxSeatsUsedChangedAtIndexToGitlabSubscriptions: reverted (0.0088s)

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