Use direct SQL to generate internal ids

What does this MR do?

Related issue: #325861 (closed)

Reimplement changes from !64240 (closed) that removes database round-trips and explicit locking when updating internal_ids. We make the assumption on generating a new value that most operations will modify existing records, so we prefer to attempt to update the row first. After some discussion, we decided to put consider putting the changes behind a feature flag, so this MR was created to do that (rather than the direct cutover in the previous MR).

Example of creation of object with internal_id, where no existing record exists (create_record!):

  Update InternalId (0.7ms)  UPDATE "internal_ids" SET "last_value" = ("internal_ids"."last_value" + 1) WHERE "internal_ids"."project_id" = 7 AND "internal_ids"."usage" = 0 RETURNING "last_value" /*application:console,line:/app/models/internal_id.rb:91:in `update_record!'*/
  TRANSACTION (0.1ms)  SAVEPOINT active_record_1 /*application:console,line:/app/models/concerns/atomic_internal_id.rb:211:in `block in project_init'*/
   (2.1ms)  SELECT MAX("issues"."iid") FROM "issues" WHERE "issues"."project_id" = 7 /*application:console,line:/app/models/concerns/atomic_internal_id.rb:211:in `block in project_init'*/
  InternalId Create (0.7ms)  INSERT INTO "internal_ids" ("project_id", "usage", "last_value") VALUES (7, 0, 1) RETURNING "id" /*application:console,line:/app/models/internal_id.rb:102:in `block in create_record!'*/

First attempts to update the existing record, and because none is found, it creates a new record. If the new record were to conflict with a concurrent insert, it retries the update.

Example of update of object with internal_id, where a record exists (update_record!):

 Update InternalId (0.3ms)  UPDATE "internal_ids" SET "last_value" = ("internal_ids"."last_value" + 1) WHERE "internal_ids"."project_id" = 7 AND "internal_ids"."usage" = 0 RETURNING "last_value" /*application:console,line:/app/models/internal_id.rb:91:in `update_record!'*/

It updates the record only.

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