[c++] Change Count operation column name

[XanthosXanthopoulos]

Issue and/or context: Resolves #4442

Changes:
Provide a different uncommon name for the Count operation to avoid conflicts with array column names

Notes for Reviewer:

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.27%. Comparing base (3d46320) to head (68afe4f).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4459      +/-   ##
==========================================
- Coverage   85.27%   85.27%   -0.01%     
==========================================
  Files         136      136              
  Lines       21266    21266              
==========================================
- Hits        18135    18134       -1     
- Misses       3131     3132       +1     

Flag	Coverage Δ
python	88.43% <ø> (-0.02%)	⬇️
r	83.53% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
python_api	88.43% <ø> (-0.02%)	⬇️
libtiledbsoma	∅ <ø> (∅)

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[jp-dark]

Fix looks good, but could you add a test that repros the bug in SOMA-938 as well?

[XanthosXanthopoulos]

Added test. With the chosen name a user can't create a column with name anyway due to prior constraints in the creation code path.