Allow increasing Meshcat kMaxPort

[nepfaff]

Is your feature request related to a problem? Please describe.
At the moment, we are limited to 100 meshcat ports, and it is not possible to close a port without exiting the script that opened them. This is limiting if I want to run lots of simulations in a script and save the meshcat recording for each of them. This is a quite common scenario for me, and I keep running into this issue.

Describe the solution you'd like
From #15618, the reason for the current limit is docker:

Yes. I've made it 7099, since that's the number of ports that the docker instances open up for meshcat (but it's all pretty arbitrary, i guess... I've rarely needed more than 2!). I've added a comment in the constructor, which I think is the right place since we may offer passing a port number as a constructor option in the future.

I would suggest adding an option to specify a custom value for kMaxPort to allow overriding the docker-motivated limit.

[ggould-tri]

Assigning @joemasterjohn as component owner.

[jwnimmer-tri]

My vote would not be for a config option, but instead to bump up our kMaxPort constant to be much larger (32767, to stop before we hit linux's ephemeral ports range).

Or if we want a config option, it would be something like meshcat_params.listen = false; which would not bind any port number. The Meshcat object then could only be used for making recordings, not anything interactive.

[jwnimmer-tri]

Once #19960 lands, the linear search range will be wider (1000 instead of 100).

More importantly for this use case, you can also specify port = 0 which will let the kernel assign a port number automatically from a pool of >16,000.