Properly Handle Custom Http Endpoints

[lou-k]

In the current version, should_use_http only returns true iff the endpoint url is in the Endpoints enum.
The register_otel function, however, accepts custom hosts as a string:

EndpointsType = Union[str, List[str], Endpoints, List[Endpoints]]

def register_otel(
    endpoints: EndpointsType,

So, if you call register_otel with an endpoint that is not in the Endpoints enum, (say, http://localhost:7000), then should_use_http will return false, even if the user intends to send things over http.

This pull request adjusts should_use_http to consider strings as input types.