Constraint support for warning case

[FikriMilano]

Is your feature request related to a problem? Please describe. Currently, constraint-extension support can only display errors. While FHIR mentions it can support errors and warnings.

Describe the solution you'd like It should also be able to display warnings.

Describe alternatives you've considered N/A

Additional context

• Need @shelaghm help on the UI design for warnings. FYI, we display errors below the field, we might want to do the same for warnings but with yellow color(?)
• Documentation of constraint Severity Types https://hl7.org/fhir/codesystem-constraint-severity.html
• Ticket for error case https://github.com/google/android-fhir/issues/1849
• PR for error case https://github.com/google/android-fhir/pull/2199

Would you like to work on the issue? Yes