Update GraphQL API to support environment detail page

Problem

Originally raised in !91573 (diffs, comment 1021201259).

It looks like deployment_approval_data is serialized for each deployment row in the environment detail page, thus find_approval_rule_for is executed for each row, which hits group.users.exists?(user.id). This could result in N+1 issue as tested.

We should reconsider the way how we serialize the data in environment detail page.

Proposal

• In deployments index page, Frontend checks if the environment is protected, and if so, the details of the protection (e.g. who can deploy/approve). We can use this query for this purpose.
• If the environment is protected and requires an approval, frontend renders the approval button in all rows. When a user clicks the button, frontend renders the approval details. We can use this query for this purpose.
• By this reason, we don't need to check find_approval_rule_for for every deployment rows. We can drop the legacy path.
• The frontend will need to be rewritten in Vue in order to use this endpoint: #23036 (closed)

A few notes:

• Batch-loading approval details with GraphQL BatchLoader would result in a very complicated process that could be another complexity and fragility point. We should avoid such process by fetching the necessary information efficiently, as described above.

Related

• PoC issue