Adding http.Client argument to the MatomoDispatcher class

[tfreebern2]

httpClient is already an argument for the MatomoDispatcher class. This PR allows the developer to pass a custom http.Client through the initialize function.

[TesteurManiak]

Why would this be needed? MatomoDispatcher is not even exposed by the library.

[tfreebern2]

Why would this be needed? MatomoDispatcher is not even exposed by the library.

The Matomo instance that my project is connected to requires certificate pinning. I've already created a fork that allows us to pass in a custom http.Client to pin the certificate required to hit the instance.