Drop unique constrain from index

What does this MR do and why?

This is the part of #427095 (closed)

This MR was extracted from !136241 (closed) because the backend part was blocked, but we need this index for other parts of the feature.

In this MR we're removing unique index and replacing with not unique as we're planning to add non-unique values to the table. That's the reason why the down migration is no-op.

Migration

We need to drop UNIQUE constraint from the index.

UP

➜  gitlab git:(427095-field-for-sbom-component) ✗ rails db:migrate VERSION=20231113171812                                              
main: == [advisory_lock_connection] object_id: 184080, pg_backend_pid: 35202
main: == 20231113171812 DropIndexFromSbomComponents: migrating ======================
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- view_exists?(:postgres_partitions)
main:    -> 0.1286s
main: -- indexes(:sbom_components)
main:    -> 0.0038s
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0003s
main: -- remove_index(:sbom_components, {:algorithm=>:concurrently, :name=>"index_source_package_names_on_component_and_purl"})
main:    -> 0.0019s
main: -- execute("RESET statement_timeout")
main:    -> 0.0002s
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- view_exists?(:postgres_partitions)
main:    -> 0.0007s
main: -- index_exists?(:sbom_components, [:component_type, :source_package_name, :purl_type], {:name=>"index_source_package_names_on_component_and_purl", :algorithm=>:concurrently})
main:    -> 0.0022s
main: -- add_index(:sbom_components, [:component_type, :source_package_name, :purl_type], {:name=>"index_source_package_names_on_component_and_purl", :algorithm=>:concurrently})
main:    -> 0.0017s
main: == 20231113171812 DropIndexFromSbomComponents: migrated (0.1601s) =============

main: == [advisory_lock_connection] object_id: 184080, pg_backend_pid: 35202

DOWN

➜  gitlab git:(427095-field-for-sbom-component) ✗ rails db:rollback:main VERSION=20231113171812
main: == [advisory_lock_connection] object_id: 183700, pg_backend_pid: 36208
main: == 20231113171812 DropIndexFromSbomComponents: reverting ======================
main: == 20231113171812 DropIndexFromSbomComponents: reverted (0.0045s) =============

main: == [advisory_lock_connection] object_id: 183700, pg_backend_pid: 36208

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Related to #427095 (closed)