feat: add filter_deleted option to avoid removing deletion markers

[v0y4g3r]

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Refer to a related PR or issue link (optional)

• Optimize compaction strategy to avoid merging SST files without overlapping time ranges #3416

What's changed and what's your intention?

This PR adds an filter_deleted option to MergeReader so that it will not remove deletion markers (or tombstones) during merging.

filter_deleted is different from dedup in that:

• If dedup is set to false, then filter_deleted will always be false since deletion markers are not expected to present.
• If dedup is set to true, then filter_deleted decides whether deletion markers should be removed.

This PR is the predecessor work of #3702.

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR does not require documentation updates.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.11%. Comparing base (bbea651) to head (dd840de).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3707      +/-   ##
==========================================
- Coverage   85.41%   85.11%   -0.31%     
==========================================
  Files         963      965       +2     
  Lines      160731   160989     +258     
==========================================
- Hits       137291   137024     -267     
- Misses      23440    23965     +525     

[fengjiachun]

LGTM