[Exporter.Geneva] Fix exemplar value serialization for TLV serialization format

[vishweshbankwar]

Fixes #.

Changes

Fixes serialization to look up the appropriate value type based on the metric type.

For significant contributions please make sure you have completed the following items:

• Appropriate CHANGELOG.md updated for non-trivial changes
• Design discussion issue #
• Changes in public API reviewed

[codecov]

Codecov Report

Attention: Patch coverage is 61.53846% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 62.92%. Comparing base (71655ce) to head (f141fb4).
Report is 222 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1698       +/-   ##
===========================================
- Coverage   73.91%   62.92%   -11.00%     
===========================================
  Files         267       35      -232     
  Lines        9615     3482     -6133     
===========================================
- Hits         7107     2191     -4916     
+ Misses       2508     1291     -1217     

Flag	Coverage Δ
unittests-Exporter.Geneva	62.92% <61.53%> (?)

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

Files	Coverage Δ
...metry.Exporter.Geneva/Metrics/TlvMetricExporter.cs	71.17% <61.53%> (ø)

... and 249 files with indirect coverage changes

[vishweshbankwar]

Received approval from component owner for merge.