value set 'http://hl7.org/fhir/us/core/ValueSet/us-core-usps-state' is empty or could not be expanded

[lmsurpre]

Is your feature request related to a problem? Please describe.
In the US Core IG, they have a ValueSet for US Postal Service states: http://hl7.org/fhir/us/core/STU4/ValueSet-us-core-usps-state.json.html

Unfortunately, the codesystem they pull from isn't defined in FHIR:

  "compose" : {
    "include" : [
      {
        "system" : "https://www.usps.com/"
      }
    ]
  }

Our current validation will therefor result in the following warning:

    {
        "severity": "warning",
        "code": "incomplete",
        "expression": ["Patient.address[0].state"],
        "details": {"text": "Membership check was not performed: value set 'http://hl7.org/fhir/us/core/ValueSet/us-core-usps-state' is empty or could not be expanded"}
    }

Describe the solution you'd like
An expanded version of this valueset available in the registry so that we can use it to validate

Describe alternatives you've considered
document how to use the remote term service provider for this codesystem

Acceptance Criteria

1. GIVEN our us-core jar is in userlib
   AND a patient resource that claims conformance to us-core-patient and has an address with a state element that has a code from http://hl7.org/fhir/us/core/ValueSet/us-core-usps-state'
   WHEN you create/update (with Prefer: return=OperationOutcome) or $validate the resource
   THEN there are no informational or warning issues about being unable to validate the code

2. GIVEN our us-core jar is in userlib
   AND a patient resource that claims conformance to us-core-patient and has an address with a state element that has a value which is not from http://hl7.org/fhir/us/core/ValueSet/us-core-usps-state'
   WHEN you create/update (with Prefer: return=OperationOutcome) or $validate the resource
   THEN there is an informational issue about being unable to validate the code

Additional context

[lmsurpre]

consider looking to package a set of pre-expanded valuesets because there are other valuesets like 'http://hl7.org/fhir/us/core/STU4/ValueSet-us-core-condition-code.html' that are even more complicated to expand (requires SNOMED CT support)

[d0roppe]

Verified that this now does not issue any warning if you use a valid USPS Code for the state