introduce additional port parameter (-p port_number) for serve command

[UBessle]

Typically i have many things running, that would like to use port 8080. So perhaps it's helpfull for others as well, if they could configure the port used by the serve command

[jp7677]

Could you please also modify the readme at https://github.com/avisi-cloud/structurizr-site-generatr/blob/main/README.md#start-a-development-web-server-around-the-generated-website and note that 8080 is the default port.

Otherwise, LGTM!

[UBessle]

build-docker failed to download ubuntu packages during Dockerfile command
RUN apt update && apt install graphviz --yes && rm -rf /var/lib/apt/lists/*

gh run view 4805742224 --log-failed shows, that some ubuntu repository server can't be reached
build-docker Build container image 2023-04-26T07:01:25.2641543Z #9 70.75 W: Failed to fetch http://ports.ubuntu.com/ubuntu-ports/dists/jammy-backports/InRelease Unable to connect to ports.ubuntu.com:80: [IP: 185.125.190.39 80]

Looks like a problem, that is not related to the content of the pull request

[jp7677]

Approved.

Please be careful with changes unrelated to the goal of a PR, in this case the additional readme formatting. Usually it works better to leave unrelated things untouched (even if they are not perfect) or to open a separate PR.
Additionally https://cbea.ms/git-commit/ might be a good read to improve your commit messages.