Suppport URL links in thePDF output

[Volodymyr Prokopyuk]

Hi Lilypond developers,

*Feature*

I'd like to request a new feature for the Lilypond program. I'd like to be
able to easily include URL links in PDF output.

*Example*

Given a URL like https://lilypond.org/ I'd like to write \link
https://lilypond.org/ in a Lilypond source and get a clickable link to the
indicated resource in the PDF output.

Thank you,
Vlad