Use search parameter filtering for search parameter disambiguation

[lmsurpre]

Is your feature request related to a problem? Please describe.
In #1272 we introduced url-based search parameter configuration in fhir-server-config.json.

However, when we build the built-in ParametersMap object, this is done outside of the context of any tenant and so we cannot really consult the tenant-specific search filter.

Further, the current ParametersMap only supports having a single search parameter per code (per resourceType).
There is some logic to warn about cases where there are multiple search parameters with the same code but differing expressions, but I thought that having multiple search parameters with the same code and equivalent expressions would be fine.

However, for our 4.5.3 release, we added some logic to SearchUtil.filterSearchParameters where, if the search parameter chosen during the initialization of the ParametersMap has a URL that differs from the one used in the tenant configuration, then the system skips over this parameter altogether.

Describe the solution you'd like

1. Update the ParametersMap to support having multiple search parameters with the same code
2. Emit warnings whenever we have conflicting search parameters and ask operators to disambiguate via fhir-server-config.json

For number 2, we used to do just this. However, since we had no mechanism for disambiguating, the logs were very frustrating because we were packaging multiple IGs with conflicting parameters. Now that we don't prepackage any IGs, I think it is reasonable to expect operators to do the disambiguation in the config when they package IGs that conflict with base spec search params.

Describe alternatives you've considered
#1625 outlines an alternative idea I had which was to build a per-tenant ParametersMap object. If we did that, then we probably wouldn't need to have ParametersMap support having multiple search parameters with the same code. However, that change seems slightly larger.

Additional context
The workaround for this issue is to avoid packaging conflicting search parameters.

[d0roppe]

Started the server and noted these messages in the log file:
[1/25/21, 17:56:11:995 UTC] 00000035 com.ibm.fhir.search.util.SearchUtil W Skipping search parameter with id='location-address'. Found multiple search parameters for code 'address' on resource type 'Location'; use search parameter filtering to disambiguate.
[1/25/21, 17:56:11:995 UTC] 00000035 com.ibm.fhir.search.util.SearchUtil W Skipping search parameter with id='location-address-state'. Found multiple search parameters for code 'address-state' on resource type 'Location'; use search parameter filtering to disambiguate.

Added the following to the fhir-server-config.json
"resources": {
"open": true,
"Location": {
"searchParameters": {
"address": "http://hl7.org/fhir/us/core/SearchParameter/us-core-location-address",
"address-state": "http://hl7.org/fhir/us/core/SearchParameter/us-core-location-address-state"
}
}
},

restarted the server, and those messages were no longer issued.