Write a blog post for v0.48.9 perf changes

[Warashi]

What this PR does / why we need it:

I wrote a blog post about the performance improvements in v0.48.9.

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

• How are users affected by this change:
• Is this breaking change:
• How to migrate (if breaking change):

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 22.82%. Comparing base (8e62937) to head (9716d2b).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5206      +/-   ##
==========================================
- Coverage   22.83%   22.82%   -0.02%     
==========================================
  Files         420      420              
  Lines       45302    45302              
==========================================
- Hits        10344    10338       -6     
- Misses      34163    34169       +6     
  Partials      795      795              

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