fix: use full endpoint in api requests

[fztgreen-veteransunited]

What this PR is for?

This PR fixes a bug where any path prefix set in the --endpoint configuration was silently discarded when building
request URLs.

When a user configured an endpoint with a path prefix (e.g. http://api-gateway/mia/), the prefix was stored correctly
in the config, but Request.URL() overwrote the full base path with the API path instead of appending to it:

// before
url.Path = r.apiPath

// after
url.Path = path.Join(url.Path, r.apiPath)

This caused all requests to be sent to the root of the host, ignoring the prefix entirely. For example, a project list
request with endpoint http://gateway/mia/ would go to http://gateway/api/backend/projects/ instead of
http://gateway/mia/api/backend/projects/.

[fztgreen-veteransunited]

Is this something we can support? It seems like a fairly large change to allow the full endpoint to be used in the api requests.

[ThisIsDemetrio]

Is this something we can support? It seems like a fairly large change to allow the full endpoint to be used in the api requests.

It is definitely an important change, but still a bugfix. It makes sense to me to use the complete endpoint instead of parsing the baseUrl without the chance to include it.

Thanks for the proposed update. I'll start an internal review and - if everything is ok - we will merge this PR in a few days.