Added the schema doc

[bashir2]

Description of what I changed

This is the first step for addressing #1025.

E2E test

TESTED:

NA

Checklist: I completed these to help reviewers :)

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• I have added tests to cover my changes. (If you refactored existing code that was well tested you do not have to add tests)

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 50.44%. Comparing base (05cf4fb) to head (d448d4b).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1087      +/-   ##
============================================
- Coverage     50.49%   50.44%   -0.06%     
+ Complexity      674      673       -1     
============================================
  Files            91       91              
  Lines          5519     5519              
  Branches        709      709              
============================================
- Hits           2787     2784       -3     
- Misses         2470     2473       +3     
  Partials        262      262              

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[chandrashekar-s]

Thanks @bashir2 for documenting this, this could be a very good reference for the FHIR-Parquet mapping. I had an initial look at it and have shared my comments. They all are minor. But I will have a one more look at it tomorrow.

[bashir2]

Thanks @chandrashekar-s for the review.

[chandrashekar-s]

Thanks @bashir2 for the changes again, the details looks good. For the example that you had asked for multiple extensions scenario, I don't have the example handy (Will update on this later). You can merge this PR in the meanwhile I guess.