Add support for R4 searches of types Timing=>Date, String=>Date

[brendankowitz]

User story
Add support for the R4 primitive types mapping to Date search type.

Acceptance criteria

1. Support is visible at the /metadata endpoint
2. Canonical urls are indexed correctly
3. Verify resources can be searched by Date. e.g. CarePlan.activity.detail.scheduled(Timing,FhirString), ChargeItem.occurrence(Timing)

[CaitlinV39]

AB#72426