Intensify operations on same key in crash test

[hx235]

Context/Summary:

Continued from #12127, we can randomly reduce the # max key to coerce more operations on the same key. My experimental run shows it surfaced more issue than just #12127.

I also randomly reduce the related parameters, write buffer size and target file base, to adapt to randomly lower number of # max key. This creates 4 situations of testing, 3 of which are new:

1. high # max key with high write buffer size and target file base (existing)
2. high # max key with low write buffer size and target file base (new, will go through some rehearsal testing to ensure we don't run out of space with many files)
3. low # max key with high write buffer size and target file base (new, keys will stay in memory longer)
4. low # max key with low write buffer size and target file base (new, experimental runs show it surfaced even more issues)

Test plan:

• [Ongoing] Rehearsal stress test
• Monitor production stress test

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[jaykorean]

LGTM!

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@hx235 merged this pull request in 5b981b6.