Add Additional Preloads to RedactionService

What does this MR do and why?

Adds missing eager-load associations to both CE and EE.

DeclarativePolicy conditions access :organization, :saml_provider, :namespace, :assignees, :author, and :system_note_metadata during Ability.allowed? checks, but these were not being eagerly loaded. This caused N+1 lazy-load queries per resource in batch authorization.

This is MR 3 of 6 in the redaction scalability series. See orbit/knowledge-graph#348 for the full plan.

How to set up and validate locally

git checkout michaelangeloio/redaction-preloads
bundle exec rails runner tmp/profile_redaction_queries.rb

See the profiling script and full results in the MR comments below.

Before (master)

PER-TYPE QUERY PROFILE (cold caches, 215 resources)
Type             Count  Queries
-----------------------------------
project              8       11
group                7       16
issue               50       63
note                50      311
work_item           50       14
milestone           50        4
-----------------------------------
TOTAL                       419

MIXED BATCH:                430

After (this MR)

PER-TYPE QUERY PROFILE (cold caches, 215 resources)
Type             Count  Queries
-----------------------------------
project              8       12
group                7       10
issue               50       17
note                50       42
work_item           50       16
milestone           50        6
-----------------------------------
TOTAL                       103

MIXED BATCH:                118

Summary

Metric	Before	After	Reduction
Mixed batch queries	430	118	72%
system_note_metadata	50 (N+1)	1 (batch)	98%
licenses	217	55	75%
saml_providers	14	8	43%

References

• Part of: orbit/knowledge-graph#348 (Improve Redaction / Auth Scalability)
• Research session: 764e8f8e (profiled 348 queries for 100 projects on postgres.ai)