Update the Prometheus Exporter to by Default not Append Timestamp

[JacksonWeber]

Which problem is this PR solving?

This PR amends the Prometheus Exporter to be in line with the text based exposition format.

Fixes #3463

Short description of the changes

Updates the default mode of the Prometheus Exporter to not append timestamp.

Type of change

Please delete options that are not relevant.

• Bug Fix (Bringing us up to spec)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• PrometheusExporter.tests
• PrometheusSerializer.tests

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[codecov]

Codecov Report

Merging #3961 (805a9ec) into main (070b685) will increase coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head 805a9ec differs from pull request most recent head af5a16b. Consider uploading reports for the commit af5a16b to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3961      +/-   ##
==========================================
+ Coverage   93.13%   93.14%   +0.01%     
==========================================
  Files         298      298              
  Lines        8869     8869              
  Branches     1826     1826              
==========================================
+ Hits         8260     8261       +1     
+ Misses        609      608       -1     

Impacted Files	Coverage Δ
...etry-exporter-prometheus/src/PrometheusExporter.ts	96.25% <ø> (ø)
...ry-exporter-prometheus/src/PrometheusSerializer.ts	95.71% <100.00%> (ø)

... and 1 file with indirect coverage changes

[legendecas]

Thank you for working on this!