What does this MR do?

NOTE: this MR is intentionally kept a bit bigger than desired to keep as much context as possible and to give a wider perspective on iteration cadences automation details.

With the above out of the way this MR addresses a couple of iteration and iteration cadence automations:

Generate iteration cadences in advance for a cadence that is set as automatic.
- This happens in 2 scenarios:
  - Cron job running on a daily basis checking for cadences that would potentially need to generate more iterations in advance. LINK TO QUERY.
  - Trigger iteration in advance generation when an iteration is being closed and roll-over issues is being attempted. We'll check if the cadence corresponding to the iteration that needs to roll-over issues has a future iteration in place.
Roll-over issues to next iteration if corresponding cadence has the roll-over flag enabled.
- This happens in a sidekiq worker and is triggered when an iteration is closed.

Database

query generated by for_automated_iterations scope

explain
SELECT "iterations_cadences".*
FROM "iterations_cadences"
WHERE "iterations_cadences"."automatic" = TRUE
	AND "iterations_cadences"."duration_in_weeks" IS NOT NULL
	AND "iterations_cadences"."duration_in_weeks" > 0
	AND ("iterations_cadences"."last_run_date" IS NULL
		OR DATE (("iterations_cadences"."last_run_date" + "iterations_cadences"."duration_in_weeks" * INTERVAL '1 week')) <= CURRENT_DATE)

Seq Scan on public.iterations_cadences  (cost=0.00..229.06 rows=1 width=111) (actual time=0.523..0.523 rows=0 loops=1)
   Filter: (iterations_cadences.automatic AND (iterations_cadences.duration_in_weeks IS NOT NULL) AND (iterations_cadences.duration_in_weeks > 0) AND ((iterations_cadences.last_run_date IS NULL) OR (date((iterations_cadences.last_run_date + ((iterations_cadences.duration_in_weeks)::double precision * '7 days'::interval))) <= CURRENT_DATE)))
   Rows Removed by Filter: 2379
   Buffers: shared hit=41
   I/O Timings: read=0.000 write=0.000

Time: 1.172 ms
  - planning: 0.612 ms
  - execution: 0.560 ms
    - I/O read: 0.000 ms
    - I/O write: 0.000 ms

Shared buffers:
  - hits: 41 (~328.00 KiB) from the buffer pool
  - reads: 0 from the OS file cache, including disk I/O
  - dirtied: 0
  - writes: 0

Adding an index:

exec create index iterations_cadences_automation on iterations_cadences USING btree (automatic, duration_in_weeks, last_run_date)

query and plan for for_automated_iterations scope after index

--same sql
explain
SELECT "iterations_cadences".*
FROM "iterations_cadences"
WHERE "iterations_cadences"."automatic" = TRUE
	AND "iterations_cadences"."duration_in_weeks" IS NOT NULL
	AND "iterations_cadences"."duration_in_weeks" > 0
	AND ("iterations_cadences"."last_run_date" IS NULL
		OR DATE (("iterations_cadences"."last_run_date" + "iterations_cadences"."duration_in_weeks" * INTERVAL '1 week')) <= CURRENT_DATE)

--slightly different plan

 Index Scan using iterations_cadences_automation on public.iterations_cadences  (cost=0.28..100.22 rows=569 width=111) (actual time=0.134..0.612 rows=892 loops=1)
   Index Cond: ((iterations_cadences.automatic = false) AND (iterations_cadences.duration_in_weeks IS NOT NULL))
   Filter: ((iterations_cadences.last_run_date IS NULL) OR (date((iterations_cadences.last_run_date + ((iterations_cadences.duration_in_weeks)::double precision * '7 days'::interval))) <= CURRENT_DATE))
   Rows Removed by Filter: 0
   Buffers: shared hit=33 read=5
   I/O Timings: read=0.122 write=0.000

Time: 1.393 ms
  - planning: 0.699 ms
  - execution: 0.694 ms
    - I/O read: 0.122 ms
    - I/O write: 0.000 ms

Shared buffers:
  - hits: 33 (~264.00 KiB) from the buffer pool
  - reads: 5 (~40.00 KiB) from the OS file cache, including disk I/O
  - dirtied: 0
  - writes: 0

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

📋 Does this MR need a changelog?
- I have included a changelog entry.
- I have not included a changelog entry because _____.
Documentation (if required)
Code review guidelines
Merge request performance guidelines
Style guides
Database guides
Separation of EE specific content

Availability and Testing

Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
Tested in all supported browsers
Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

Label as security and @ mention @gitlab-com/gl-security/appsec
The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
Security reports checked/validated by a reviewer from the AppSec team

Draft: Add auto-generation of iterations for iteration cadences