Epic: reduce space amplification

[shanyp]

Motivation

DoD

Implementation ideas

Tasks

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1. perf: high read amplification #4377
   c/storage/pageserver +1
2. perf: high space amplification #4376
   c/storage/pageserver +1
3. perf: parallel load layer map #4400
   a/performance c/storage/pageserver t/feature +3
4. Add pageserver component perf tests #1380
   a/benchmark a/performance a/test c/storage/pageserver +4
   
5. More concurrency for compaction #1359
   c/storage c/storage/pageserver +2
6. No WALs can be directly redone in page server for pg_bench simple_update? #4349
   t/bug +1
7. Epic: Partial Fetch from S3 #4348
   c/storage t/Epic +2
8. local manifest for atomic storage operation #4418
   a/tech_debt c/storage +2
   
9. avoid using layers map lock for file deletion #4509
   c/storage/pageserver +1
10. correctly record l0 delta layer key range #4553
    a/performance c/storage c/storage/pageserver t/feature +4
11. incremental compaction / image layer generation #4580
    c/storage/pageserver t/feature +2
12. refactor: in-memory immutable storage state #4373
    a/reliability c/storage c/storage/pageserver +3
    

Other related tasks and Epics

[jcsp]

Ongoing compaction work is in #6768