Add support for subdomain in jupyterlab module

[framctr]

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Reference issue #313

[framctr]

I changed also the prints in the run.sh to be compatible with /bin/sh according to https://www.shellcheck.net/wiki/SC2028

[matifali]

Hi @framctr, do you plan to finish this? If not, I can help complete this. Thank you :)

[framctr]

@matifali As I said previously, I cannot verify with subdomain=true and for this reason, I didn't update anything more. If you can verify this it would be great. 😊

Anyway, I can do a final check with the last changes with subdomain false.

[matifali]

I left a few comments and suggestions on possible issues with url.