Add index for searching environments name without type

What does this MR do and why?

Adding an index for the change in Fix search within Environments folder (!146154 - merged).

The old query has a custom index introduced here: !102227 (diffs)

So we are adding a custom index for the new query as well since it is recommended by Database Labs.

Before (Old Query)

SELECT "environments".* FROM "environments" 
WHERE "environments"."project_id" = 49114813 
AND (LOWER(ltrim(environments.name, environments.environment_type || '/')) LIKE LOWER('podtato') || '%') LIMIT 5

After (New Query)

SELECT "environments".* FROM "environments" 
WHERE "environments"."project_id" = 49114813 
AND (LOWER(ltrim(ltrim(environments.name, environments.environment_type), '/')) LIKE LOWER('podtato') || '%') LIMIT 5

MR acceptance checklist

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Screenshots or screen recordings

DB migration output

$ bundle exec rails db:migrate
main: == [advisory_lock_connection] object_id: 119420, pg_backend_pid: 14196
main: == 20240229223236 AddIndexEnvironmentsNameWithoutType: migrating ==============
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- view_exists?(:postgres_partitions)
main:    -> 0.0147s
main: -- index_exists?(:environments, "project_id, lower(ltrim(ltrim(name, environment_type), '/')) varchar_pattern_ops, state", {:name=>"index_environments_name_without_type", :algorithm=>:concurrently})
main:    -> 0.0043s
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0002s
main: -- add_index(:environments, "project_id, lower(ltrim(ltrim(name, environment_type), '/')) varchar_pattern_ops, state", {:name=>"index_environments_name_without_type", :algorithm=>:concurrently})
main:    -> 0.0027s
main: -- execute("RESET statement_timeout")
main:    -> 0.0002s
main: == 20240229223236 AddIndexEnvironmentsNameWithoutType: migrated (0.0336s) =====

main: == [advisory_lock_connection] object_id: 119420, pg_backend_pid: 14196

How to set up and validate locally

Run the migration:

bundle exec rails db:migrate

Related to #427537 (closed)