PR request: Variable hub port

[ErrorProne]

I've a small change to make the selenium hub port variable for which I would like to open a pull request main...ErrorProne:testbench:variableHubPort

Right now one is forced to the default 4444 port. This can be problematic in some cases, for example in shared docker environments in CI pipelines, and could lead to conflicting port mappings. It is also discouraged by libs like testcontainers which actively try to avoid mapping fixed ports to the docker host (still possible to do tho).