docs: add Supermetal to known users

[kumarUjjawal]

Which issue does this PR close?

• Closes #.

Rationale for this change

About Supermetal:

Supermetal is a change data capture (CDC) platform that synchronizes data between databases, data warehouses, and lakehouses while preserving transactional consistency. It handles low latency streaming and large scale batch movement with exceptional compute efficiency, replicating terabytes on hardware as small as a 2 vCPU, 8GB instance.

It ships as a single binary with no external dependencies and runs anywhere, on premise, hybrid, or multi cloud.

What changes are included in this PR?

Adds Supermetal (https://supermetal.io/), a change data capture platform, to the list of known DataFusion users.

Are these changes tested?

Yes

Are there any user-facing changes?

No

[kumarUjjawal]

Disclaimer: I work for Supermetal Inc.

[kumarUjjawal]

Thank you @xudong963

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.71%. Comparing base (5de7f1d) to head (e8610a7).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #23790      +/-   ##
==========================================
- Coverage   80.71%   80.71%   -0.01%     
==========================================
  Files        1089     1089              
  Lines      368760   368760              
  Branches   368760   368760              
==========================================
- Hits       297647   297631      -16     
- Misses      53372    53382      +10     
- Partials    17741    17747       +6     

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