Implementing $includes operation with paging.

[tarunmathew12]

Description

The PR contains the implementation of the $includes operation (explained in the spec below) including UT/E2E tests.

[$includes operation spec]
https://microsoft.sharepoint.com/:w:/t/msh/EaYsMkWJsVxNpaHhokCQbQcBxHtWbL8u80sTsENnKYNnPA?e=O1gE7h

Related issues

Addresses [issue #138967].
User Story 138967: Implement a new $include operation.

Testing

Manually tested. Automated tests being added.

FHIR Team Checklist

• Update the title of the PR to be succinct and less than 65 characters
• Add a milestone to the PR for the sprint that it is merged (i.e. add S47)
• Tag the PR with the type of update: Bug, Build, Dependencies, Enhancement, New-Feature or Documentation
• Tag the PR with Open source, Azure API for FHIR (CosmosDB or common code) or Azure Healthcare APIs (SQL or common code) to specify where this change is intended to be released.
• Tag the PR with Schema Version backward compatible or Schema Version backward incompatible or Schema Version unchanged if this adds or updates Sql script which is/is not backward compatible with the code.
• CI is green before merge
• Review squash-merge requirements

Semver Change (docs)

Patch|Skip|Feature|Breaking (reason)

[tarunmathew12]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[tarunmathew12]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[LTA-Thinking]

Why move this from API to Core?

[tarunmathew12]

Route names are needed to create the related link in a bundle response. For example, when a number of included resources exceeds the max count (CoreFeatureConfiguration.DefaultIncludeCountPerSearch) for an initial search request (e.g. "GET {{hostname}}/Patient?_revinclude=..."), the related link for $includes must be created in a bundle response that requires a different route name ("Includes") than one for the search request being processed ("SearchResources") since the related link will look like "{{hostname}}/Patient/$includes?_revinclude=". (Please check changes in BundleFactory.CreateLink.)
I chose to move the file (and a few others) to Core over hardcoding the route name. Please let me know if you have any suggestions. Thank you.

[LTA-Thinking]

Is an include CT valid without the two include values?

[tarunmathew12]

Yes, when the includes continuation token is created for an initial search request, these two values for include resources are null, so a bundle response for the 1st $includes request will contain included resources from the beginning (an included resource with the smallest resource type id and surrogate id).
Please note that a bundle response for the initial search request will not have any included resources if its number exceeds the include count in appsettings per conversation with Brendan and Jared.