Changes to fix issues of missing extensions and others

[chandrashekar-s]

Description of what I changed

Fixes #1027 The below mentioned changes have been made as part of this PR

• Handled the error properly when the StructureDefinitions for extensions are missing.
• The DoubleConverter for decimal data types has been fixed, which was failing for Leaf Extensions containing Decimal data types.
• The avro schema name for the Reference types have been changed to contain a full path name from root, so that it is unique for each path.

E2E test

• Tested the changes by referencing an extension whose StructureDefinition was not available and ensure proper error message is thrown instead of NPE.
• Ingested an QuestionnaireResponse fhir resource and ran a Full Run and checked if the QuestionnaireResponse is converted to Avro record properly

TESTED:

• Added a unit test case

Checklist: I completed these to help reviewers :)

• [x] I have read and will follow the review process.

• [x] I am familiar with Google Style Guides for the language I have coded in.

  No? Please take some time and review Java and Python style guides.

• [x] My IDE is configured to follow the Google code styles.

  No? Unsure? -> configure your IDE.

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

• [x] I ran mvn clean package right before creating this pull request and added all formatting changes to my commit.

• [x] All new and existing tests passed.

• [x] My pull request is based on the latest changes of the master branch.

  No? Unsure? -> execute command git pull --rebase upstream master

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 70.00000% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 50.60%. Comparing base (498d7c1) to head (bebc984).

Files	Patch %	Lines
.../bunsen/definitions/r4/R4StructureDefinitions.java	50.00%	2 Missing and 1 partial :warning:
...sen/definitions/stu3/Stu3StructureDefinitions.java	50.00%	2 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1050 +/- ## ============================================ - Coverage 50.60% 50.60% -0.01% - Complexity 673 674 +1 ============================================ Files 91 91 Lines 5505 5511 +6 Branches 707 707 ============================================ + Hits 2786 2789 +3 - Misses 2457 2461 +4 + Partials 262 261 -1 ```

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[chandrashekar-s]

Hi @bashir2, thanks for the review. I have updated my comments and I have also created these 2 issues (Relook at the recursive depth and Fix the number of parquet files for DirectRunner) which can be resolved in different PRs.

[chandrashekar-s]

Thanks @bashir2 for the review, I have addressed the review comments and will be merging the PR. Please let me know if you see any discrepancies and I will take them up in a separate PR.