Diagnostic report resource added

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 98.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 97.71%. Comparing base (627c07e) to head (e721389). Report is 1 commits behind head on main.

Files	Patch %	Lines
fhirflat/resources/diagnosticreport.py	96.42%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #65 +/- ## ======================================= Coverage 97.70% 97.71% ======================================= Files 40 42 +2 Lines 1962 2010 +48 ======================================= + Hits 1917 1964 +47 - Misses 45 46 +1 ```

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