Index deployments table for DeploymentsFinder's query performance

What does this MR do and why?

Create index_deployments_on_project_id_and_environment_id_and_status_and_finished_at to resolve #357648 (closed)

We also checked index_deployments_for_visible_scope implemented in !83498 (merged) but observed it is not useful.

How to set up and validate locally

rails db:migrate:up VERSION=20220404140813

== 20220404140813 PrepareIndexProjectIdEnvironmentIdStatusFinishedAtOnDeployments: migrating
-- transaction_open?()
   -> 0.0000s
-- index_exists?(:deployments, [:project_id, :environment_id, :status, :finished_at], {:name=>"index_deployments_on_project_environment_status_and_finished_at", :algorithm=>:concurrently})
   -> 0.0104s
-- execute("SET statement_timeout TO 0")
   -> 0.0005s
-- add_index(:deployments, [:project_id, :environment_id, :status, :finished_at], {:name=>"index_deployments_on_project_environment_status_and_finished_at", :algorithm=>:concurrently})
   -> 0.0077s
-- execute("RESET statement_timeout")
   -> 0.0006s
== 20220404140813 PrepareIndexProjectIdEnvironmentIdStatusFinishedAtOnDeployments: migrated (0.0274s)

rails db:migrate:down VERSION=20220404140813

== 20220404140813 PrepareIndexProjectIdEnvironmentIdStatusFinishedAtOnDeployments: reverting
-- transaction_open?()
   -> 0.0000s
-- indexes(:deployments)
   -> 0.0095s
-- execute("SET statement_timeout TO 0")
   -> 0.0005s
-- remove_index(:deployments, {:algorithm=>:concurrently, :name=>"index_deployments_on_project_environment_status_and_finished_at"})
   -> 0.0036s
-- execute("RESET statement_timeout")
   -> 0.0005s
== 20220404140813 PrepareIndexProjectIdEnvironmentIdStatusFinishedAtOnDeployments: reverted (0.0207s)

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.

Related to #357648 (closed)