docs: Add design document about enhanced queueing for pessimistic lock contention

[MyonKeminta]

Signed-off-by: MyonKeminta [email protected]

What problem does this PR solve?

Issue Number: ref tikv/tikv#13298

Based on tikv/rfcs#100

Problem Summary:

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.0412%. Comparing base (b9dc386) to head (e5b166b).
Report is 3580 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #37518        +/-   ##
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+ Coverage   73.6330%   81.0412%   +7.4082%     
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  Files          1151       2638      +1487     
  Lines        362290     717923    +355633     
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+ Hits         266765     581814    +315049     
- Misses        78344     113129     +34785     
- Partials      17181      22980      +5799