[chore][samplereceiver] Update internal telemetry metric units

[crobert-1]

Description

Update telemetry units to be more clear. Related to #10658, we may be blocked here waiting for official units to use.

Note: I've kept one metric with the unit "1", as it's not meant to be meaningful, just to show a metric that's disabled by default.

Since this code is internal and only used for tests, from what I can tell, I don't believe we need a changelog entry.

Link to tracking issue

Fixes #10653

[codeboten]

It looks like some tests will need to be updated

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.17%. Comparing base (458c4f9) to head (09b69a6).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #10672   +/-   ##
=======================================
  Coverage   92.17%   92.17%           
=======================================
  Files         401      401           
  Lines       18786    18786           
=======================================
  Hits        17316    17316           
  Misses       1110     1110           
  Partials      360      360           

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