$process-message operation on FhirClient

[LodewijkSioen]

Is your feature request related to a problem? Please describe.
We're working with FHIR messaging. For this we opted to use the $process-message operation. This line in the specifications is giving me headaches:

This operation does not use the parameters resource; the parameters "async" and "response-url" always go in the URL, if they are used, and the "content" parameter is always the body of the HTTP message.

I don't think it is possible to do this with the FhirClient. All the operation-based functions take a Parameter object and post it to the server.
cf #2601

Describe the solution you'd like

public virtual Task<Bundle?> ProcessMessageAsync(Bundle bundle, bool async = false, string responseUrl = null, CancellationToken? ct = null)

Describe alternatives you've considered
Not using the FhirClient and do everything using the vanilla HttpClient :(

[LodewijkSioen]

Would you accept a PR for this? If so, is there a process for this?

[LodewijkSioen]

I went ahead and just did it ;)

[mmsmits]

Thanks @LodewijkSioen, this is greatly appreciated.
I'll take a look at this.

Sorry for not responding to your question earlier.

[LodewijkSioen]

@mmsmits no problem. What is the release schedule for the SDK?

[mmsmits]

Normally, we release once every month or so, but I'm not sure we'll get one before Christmas.
In the mean time, you can always use a pre-release package. The package with your PR will appear here within 45 minutes or so. https://github.com/FirelyTeam/firely-net-sdk/pkgs/nuget/Hl7.Fhir.R4/versions

Note: this can also contain other changes, they are a representation of the current develop branch