Update content-type for mappings to v3

[TimHess]

Description

Remove the override that forced mappings label responses as v2.
Also throw an exception if SBA url wasn't set rather than trying to connect first.

Quality checklist

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• You've updated unit and/or integration tests for your change, where applicable.
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[TimHess]

Tested with SBA 3.4.3 built from SteeltoeOSS/Dockerfiles#42

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud