doc: help2man: convert OSC hyperlinks

doc: help2man: convert OSC hyperlinks

* man/help2man: Convert OSC hyperlinks to roff \X escapes,
which will be converted back to OSC hyperlinks when
the man page is displayed on the terminal.
Note formatting is removed from hyperlinked text by default,
thus relying on how the terminal highlights hyperlinks,
but --bold-refs is honored in this case, in which hyperlinked
text will be marked up as bold, which matches the default
markup used for non hyperlinked options.