Is your feature request related to a problem? Please describe.
The current GHC/Probe implementation uses default HTTP User-Agent from the Python libs. This is not a web-friendly way to invoke remote web-services.

Describe the solution you'd like
Send a clear User-Agent header denoting the GHC project

Describe alternatives you've considered
N.A.

Additional context
May even add version info. See for example OWSLib:

REQUEST_HEADERS = {
    'User-Agent': 'OWSLib {} (https://geopython.github.io/OWSLib)'.format(__version__)
}

Probe.get_request_headers() is the central function responsible for setting HTTP request headers.
Here at least we need to set User-Agent.

Also in the function healthcheck.py:sniff_test_resource() remote services are called.