Added custom search example for sort by date

[mikaelweave]

Description

Add a REST doc showing how you can achieve sort on a custom Search Parameter.

Related issues

#3616

Testing

Ran through REST client in VSCode vs localhost SQL.

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)

[LTA-Thinking]

What do these extra examples show? I don't see a search parameter for them or examples using them.

[mikaelweave]

Good catch - updated to be more obvious that the "extra resource" is to show null behavior without :missing.

[rajithaalurims]

As @mikaelweave and I discussed, we still need to fix SQL that is generating to get null values when missing modifier on sort parameter is specified.