Add telemetry point for null file content

[0xnm]

What does this PR do?

This is an additional telemetry point for the issue, when sometimes file content is only "\u0000" (happens when we decode information for NDK crash submission).

I didn't manage to understand why it happens. In theory if decoding from bytes to string fails, broken chars should be mapped to \ufffd, but to validate the assumption that the issue is on during decoding I'm adding this.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)

[codecov-commenter]

Codecov Report

Merging #1792 (96d45a1) into develop (9eefcc4) will decrease coverage by 0.28%.
Report is 2 commits behind head on develop.
The diff coverage is 14.29%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1792      +/-   ##
===========================================
- Coverage    83.64%   83.37%   -0.28%     
===========================================
  Files          466      466              
  Lines        16368    16372       +4     
  Branches      2451     2452       +1     
===========================================
- Hits         13691    13649      -42     
- Misses        2023     2044      +21     
- Partials       654      679      +25     

Files	Coverage Δ
...dog/android/ndk/internal/DatadogNdkCrashHandler.kt	80.81% <14.29%> (-2.92%)	⬇️

... and 24 files with indirect coverage changes