Unit Test: HTTP Client

[EricWittmann]

We have had numerous problems with Java HTTP clients not properly working with some URLs, specifically from GitLab. As a result, I'm always hesitant to upgrade the version of the HTTP client we're using. To increase confidence, we should create a simple unit test that does the following:

1. start up an echo HTTP server
2. make problematic HTTP calls using the apicurio http client
3. assert that the echo response is what it should be

An example of a problematic gitlab endpoint is:

https://docs.gitlab.com/ee/api/repository_files.html#get-file-from-repository

The file_path component of the URL must be an encoded file path. But many of the HTTP clients end up mangling the URL and un-encoding the path, which is then not recognized by GitLab.