Adds 'requiredPorts' functionality

[christophergunn]

I find people often have processes running locally which have port usages similar to those that we wish to spin-up via this library. E.g. a local proxy to a cloud instance of the DB which their app uses. This leads to annoyance and hunting through sometimes cryptic docker compose log lines to discover a simple problem which could have been proactively checked for (fast-fail) prior to docker compose up being invoked.

This PR introduces an optional property 'RequiredPorts' which will be checked for before running docker compose up. If any ports are found to be in use, a custom exception is raised and the clashing ports are surfaced on the 'Ports' property of this exception instance.