[PLAT-5608]: Automatically add the correct suffix to endpoint

[bengourley]

Goal

Only accepting the full/absolute URL meant that On-Premise needed to know unecessary detail about the different paths on the upload server, and also meant some commands were unnecessarily repetitive:

bugsnag-source-maps upload-react-native --endpoint https://bugsnag.my-company.com/react-native-source-map ...

Design

Based on the kind of source map being uploaded (which we know becuase there is a separate command/library for each) we can predict what the path of the URL is: either /sourcemap¹ or /react-native-source-map

¹ the path /source-map exists (which is correctly named) but for now we use /sourcemap – it has existed for longer so supports older On-Premise versions.

Changeset

• Added a small utility to build the full endpoint URL
• Ensured backward compatibility is maintained (e.g. if the --endpoint provided includes a path longer than /, it will use that verbatim)

Testing

Updated unit tests.