Add database indexes for hashed columns in user_credit_card_validations

What does this MR do and why?

• Pre-requisite for sub-task 2 of https://gitlab.com/gitlab-org/gitlab/-/issues/413525 and follows from discussion !131365 (comment 1590623278).
• Before using the hashed columns to compare credit-card records, we need to add the database indexes on the hashed columns.
• Methods similar_holder_names_count and used_by_banned_user? will use the index on holder_name_hash
• Method similar_records will use the index on (expiration_date_hash, last_digits_hash, network_hash, credit_card_validated_at)

Database

• There are a total 160K records in the user_credit_card_validations table
• We currently have 2 existing indexes on the table -
  • (expiration_date, last_digits, network, credit_card_validated_at). To match this, an index on (expiration_date_hash, last_digits_hash, network_hash, credit_card_validated_at) has been added.
    • query plan for similar_records
  • (lower(holder_name), expiration_date, last_digits, credit_card_validated_at). To match this, an index on only (holder_name_hash) has been added.
    • Because the query plan for used_by_banned_user? with the full index on has similar performance to the query plan for used_by_banned_user? with a index only on holder_name_hash
    • query plan for similar_holder_names_count

Output of db:migrate

main: == 20231009104202 AddHolderNameHashIndexOnCreditCardValidations: migrating ====
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- view_exists?(:postgres_partitions)
main:    -> 0.0013s
main: -- index_exists?(:user_credit_card_validations, :holder_name_hash, {:name=>"idx_user_credit_card_validations_on_holder_name_hash", :algorithm=>:concurrently})
main:    -> 0.0040s
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0006s
main: -- add_index(:user_credit_card_validations, :holder_name_hash, {:name=>"idx_user_credit_card_validations_on_holder_name_hash", :algorithm=>:concurrently})
main:    -> 0.0018s
main: -- execute("RESET statement_timeout")
main:    -> 0.0006s
main: == 20231009104202 AddHolderNameHashIndexOnCreditCardValidations: migrated (0.0240s) 
main: == [advisory_lock_connection] object_id: 41184540, pg_backend_pid: 11045
main: == [advisory_lock_connection] object_id: 41234780, pg_backend_pid: 11050
main: == 20231009104325 AddPartialMatchIndexOfHashesOnCreditCardValidations: migrating 
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- view_exists?(:postgres_partitions)
main:    -> 0.0018s
main: -- index_exists?(:user_credit_card_validations, [:expiration_date_hash, :last_digits_hash, :network_hash, :credit_card_validated_at], {:name=>"idx_user_credit_card_validations_partial_match_of_hashes", :algorithm=>:concurrently})
main:    -> 0.0053s
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0006s
main: -- add_index(:user_credit_card_validations, [:expiration_date_hash, :last_digits_hash, :network_hash, :credit_card_validated_at], {:name=>"idx_user_credit_card_validations_partial_match_of_hashes", :algorithm=>:concurrently})
main:    -> 0.0022s
main: -- execute("RESET statement_timeout")
main:    -> 0.0006s
main: == 20231009104325 AddPartialMatchIndexOfHashesOnCreditCardValidations: migrated (0.0274s) 
main: == [advisory_lock_connection] object_id: 41234780, pg_backend_pid: 11050

Output of db:rollback

main: == 20231009104325 AddPartialMatchIndexOfHashesOnCreditCardValidations: reverting 
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- view_exists?(:postgres_partitions)
main:    -> 0.0245s
main: -- indexes(:user_credit_card_validations)
main:    -> 0.0055s
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0006s
main: -- remove_index(:user_credit_card_validations, {:algorithm=>:concurrently, :name=>"idx_user_credit_card_validations_partial_match_of_hashes"})
main:    -> 0.0014s
main: -- execute("RESET statement_timeout")
main:    -> 0.0005s
main: == 20231009104325 AddPartialMatchIndexOfHashesOnCreditCardValidations: reverted (0.0578s) 

main: == 20231009104202 AddHolderNameHashIndexOnCreditCardValidations: reverting ====
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- view_exists?(:postgres_partitions)
main:    -> 0.0009s
main: -- indexes(:user_credit_card_validations)
main:    -> 0.0032s
main: -- remove_index(:user_credit_card_validations, {:algorithm=>:concurrently, :name=>"idx_user_credit_card_validations_on_holder_name_hash"})
main:    -> 0.0011s
main: == 20231009104202 AddHolderNameHashIndexOnCreditCardValidations: reverted (0.0193s) 

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Related to #413525