Use public fire.ly server in tests

[devmotion]

This PR fixes the (probably temporary) test errors caused by the HAPI FHIR server errors by switching to the public fire.ly server in our tests.

Fixes #134.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (7f2b171) 100.00% compared to head (ab27918) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #135   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            8         8           
  Lines          187       187           
=========================================
  Hits           187       187           

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[DilumAluthge]

I wonder if this is a good time to refactor our test suite and factor all of the test-server-specific values out.

So e.g. we could define a struct inside of test/runtests.jl of the form:

Base.@kwdef struct TestFHIRServer
    base_url::String
    patient_firstname::String
    ...
end

Then, the other parts of the test suite will just extract the values from the TestFHIRServer struct.

And then, in order to switch test servers, we only need to change the values in one place.

[devmotion]

I'm not sure if it's worth it since we only use the server in two places. Additionally, I thought about using a different query for testing pagination - for the current tests, I looked up a query that returned only very few results, all with a proper ID, but for pagination tests many search results would be desirable.

[DilumAluthge]

I'll just put it into an issue for now: #136