This mock Segment server can be used to test our extension metrics. It
will respond to all request with HTTP 200, and will print the requests
to the console. It also has parsing built-in for Segment request
payloads.
Right now only the event name is printed, but we can enhance this in
the future to print more event information. We can also enhance the
mock to be a more realistic representation of the API.
The extension has been modified to allow the Segment host to be
overwritten with the `SEGMENT_HOST` environment variable. This will
ensure that all Segment events are redirected to that host.
So for example, to create a dev build that uses this server, you could
set the `SEGMENT_WRITE_KEY` and `SEGMENT_LEGACY_WRITE_KEY` values to
any non-empty string, and set `SEGMENT_HOST` to
`http://localhost:9090`.
This was created originally to test PR #9768
