Add FK for deployments.environment_id to environments table

What does this MR do?

There is a data integrity issue on deployments table that deployments.environment_id doesn't have a foreign key, so there are some orphaned deployments reported.

This MR adds the foreign key to stop creating orphaned deployments. This is long overdue.

FYI, the environment_id is indexed and has NOT NULL constraint already.

Related #26229 (closed)

Migration test on db-lab

exec ALTER TABLE deployments
ADD CONSTRAINT fk_009fd21147
FOREIGN KEY (environment_id)
REFERENCES environments (id)
ON DELETE CASCADE
NOT VALID;

The query has been executed. Duration: 31.715 ms (edited)

https://gitlab.slack.com/archives/CLJMDRD8C/p1624515683213100

The following query - the validation on all rows, won't be performed due to the orphaned rows. See !64585 (comment 609380270) for more info.

exec ALTER TABLE deployments VALIDATE CONSTRAINT fk_009fd21147;

Migration test on local environment

shinya@shinya-B550-VISION-D:~/workspace/thin-gdk/services/rails/src$ tre bin/rails db:migrate:redo VERSION=20210622135221
INFO: This script is a predefined script in devkitkat.
== 20210622135221 AddForeignKeyForEnvironmentIdToEnvironments: reverting ======
-- foreign_keys(:deployments)
   -> 0.0022s
-- remove_foreign_key(:deployments, :environments)
   -> 0.0033s
== 20210622135221 AddForeignKeyForEnvironmentIdToEnvironments: reverted (0.0094s) 

== 20210622135221 AddForeignKeyForEnvironmentIdToEnvironments: migrating ======
-- transaction_open?()
   -> 0.0000s
-- foreign_keys(:deployments)
   -> 0.0022s
-- execute("ALTER TABLE deployments\nADD CONSTRAINT fk_009fd21147\nFOREIGN KEY (environment_id)\nREFERENCES environments (id)\nON DELETE CASCADE\nNOT VALID;\n")
   -> 0.0039s
== 20210622135221 AddForeignKeyForEnvironmentIdToEnvironments: migrated (0.0094s) 

Does this MR meet the acceptance criteria?

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Security

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