httpserver should not use boost::program_options

[nyh]

modules/httpserver-api uses boost::program_options to do some trivial option parsing that could have easily been done using getopt_long (see how we did that for another small utility, cpiod.so, in #980).

As explained in #1040, we can no longer assume that the OSv exports the program_options symbols, so httpserver will now need to come with a copy of libboost_program_options.so, which both complicates its manifest and adds about 1MB to the size of the image. But either easier than doing that (adding this .so to the image), we can simply stop using boost::program_options there.