feat: add Batch support

[ssvegaraju]

Issue #, if available:

Description of changes:
Added logic to parse requests made to the root URL with a Batch request. Contains logic to validate the bundle according to https://www.hl7.org/fhir/http.html#brules, and adds unit tests for batch. This PR is in draft until the persistence changes are released and updated on the interface package.

We use a limit of 750 requests per bundle for the following reason:
Lambda has a payload limit of 6MB. Taking an average request size of 4KB, this gives us that 6MB/4KB = 1500 requests. To give some leeway, we divide by half to get 750.

TESTING:
tested through deployment and querying for various different bundle configurations such as:

• batches with references to resource within the bundle
• all different CRUD operations
• failing CRUD operations should not affect bundle success

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Merging #162 (61c83f2) into mainline (1108326) will increase coverage by 0.17%.
The diff coverage is 92.85%.

@@             Coverage Diff              @@
##           mainline     #162      +/-   ##
============================================
+ Coverage     75.76%   75.93%   +0.17%     
============================================
  Files            47       47              
  Lines          1366     1384      +18     
  Branches        284      296      +12     
============================================
+ Hits           1035     1051      +16     
- Misses          331      333       +2     

Impacted Files	Coverage Δ
src/router/bundle/bundleParser.ts	98.37% <80.00%> (-0.53%)	⬇️
src/router/bundle/bundleGenerator.ts	94.11% <87.50%> (-1.44%)	⬇️
src/router/bundle/bundleHandler.ts	91.66% <100.00%> (+1.12%)	⬆️

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[Bingjiling]

Looks good! Some last changes for generateBatchBundle and we're good to go.

[Bingjiling]

Put this logic in Persistence instead of here? If etag and lastModified should not exist, it is Persistence's responsibility to remove them instead of depending on another package to handle it.

[ssvegaraju]

I don't think it's possible to remove the vid/lastmodified fields from the persistence response as they are a required property of the type. However, I removed the logic to explicitly remove them, and instead combined the logic with the transaction bundle generation.