Docs: Include info about numerical type used in metrics in telemetry.md

[agehrke]

Pull Request

This PR adds info about the numerical type used for the three metrics. This is useful to know if you use the MeterListener class which requires you to specify the measurement type when calling SetMeasurementEventCallback<T>().

The issue or feature being addressed

Improve documentation of metrics.

Details on the issue fix or feature implementation

Confirm the following

• I started this PR by branching from the head of the default branch
• I have targeted the PR to merge into the default branch
• I have included unit tests for the issue/feature
• I have successfully run a local build

[agehrke]

@dotnet-policy-service agree

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (6ce4ee0) 84.63% compared to head (a8e9968) 84.63%.
Report is 1 commits behind head on main.

Additional details and impacted files

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  Coverage   84.63%   84.63%           
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  Files         306      306           
  Lines        6819     6819           
  Branches     1045     1045           
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  Hits         5771     5771           
  Misses        839      839           
  Partials      209      209           

Flag	Coverage Δ
linux	?
macos	84.63% <ø> (ø)
windows	84.63% <ø> (ø)

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