Add abillity to set path prefix

[mkroman]

This PR should replace the --random-route argument with both a --path-prefix argument and a conflicting --random-path-prefix argument.

I use miniserve behind a load-balancer under a specific path, so I need to control the path in miniserves web server, but while I can show the index page in a subdirectory, the links in the file index aren't relative to the current URL.

Here's an example - the indexed file links don't work because it assumes the relative URL path is / and it will link to the root domain accordingly (i.e. not under /pub/)

The --random-path-prefix argument should be a fully functional replacement to --random-route. More testing may be required.

[svenstaro]

Sorry, I know I've been slacking on this. Could you rebase this for recent master changes, please?

[svenstaro]

@mkroman In addition to rebasing this, is there any chance I can convince you to make a test for this? :)

[bjeanes]

It seems like the author of this PR has probably abandoned the effort, but I'd like to weigh in that I also have been trying to run miniserve behind a reverse proxy with a path prefix (which, unfortunately, is required). Any possibility that this is something you'd likely consider doing @svenstaro ?

[svenstaro]

Sure, I'd still like for something like this to go in. Do you wanna take a stab at it, @bjeanes?

[bjeanes]

Yeah I'd consider taking a stab on the weekend if I don't spend the time away from computer. But in full transparency, I opted to use rclone serve http with its base path option since leaving my comment so my immediate need has diminished. However I definitely would like the tgz/zip feature for this use case, so there is still some motivation :)

[svenstaro]

Anyone interested in cleaning this up, rebasing it, and getting it in? :)

[Jikstra]

I reimplemented this on top of the main branch #579

[svenstaro]

Closing in favor of #579.