Recalculate UUID for all Vulnerability::Findings, attempt 1

What does this MR do?

In !46483 (merged) we have started calculating UUIDv5 for new Findings instead of using just time-based UUIDs. This will schedule a background data migration to recalculate all UUIDs so our Feedback <-> Finding matching is more stable.

Query details

rails db:migrate

== 20201112130715 ScheduleRecalculateUuidOnVulnerabilitiesOccurrences: migrating
-- Scheduling RecalculateVulnerabilitiesOccurrencesUuid jobs
== 20201112130715 ScheduleRecalculateUuidOnVulnerabilitiesOccurrences: migrated (0.0112s)

Modifying one record using BulkImport

https://explain.dalibo.com/plan/CEa

Execution plan and timings

 ModifyTable on public.vulnerability_occurrences  (cost=0.44..3.48 rows=1 width=1304) (actual time=56.287..56.291 rows=0 loops=1)
   Buffers: shared hit=25 read=39 dirtied=11
   I/O Timings: read=55.419
   CTE cte
     ->  Result  (cost=0.00..0.01 rows=1 width=98) (actual time=0.002..0.003 rows=1 loops=1)
   ->  Nested Loop  (cost=0.43..3.47 rows=1 width=1304) (actual time=7.115..7.121 rows=1 loops=1)
         Buffers: shared read=4
         I/O Timings: read=7.047
         ->  CTE Scan on cte  (cost=0.00..0.02 rows=1 width=220) (actual time=0.018..0.021 rows=1 loops=1)
         ->  Index Scan using vulnerability_occurrences_pkey on public.vulnerability_occurrences  (cost=0.43..3.45 rows=1 width=1092) (actual time=7.092..7.093 rows=1 loops=1)
               Index Cond: (vulnerability_occurrences.id = cte.cte_id)
               Buffers: shared read=4
               I/O Timings: read=7.047

Time: 56.743 ms
  - planning: 0.332 ms
  - execution: 56.411 ms
    - I/O read: 55.419 ms
    - I/O write: 0.000 ms

Shared buffers:
  - hits: 25 (~200.00 KiB) from the buffer pool
  - reads: 39 (~312.00 KiB) from the OS file cache, including disk I/O
  - dirtied: 11 (~88.00 KiB)
  - writes: 0

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• 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

Related to #212322 (closed)