[IMP] server: rename xmlrpc* related parameters

The 'xmlrpc'-based configuration parameters have been a misnomer since
the introduction of the generic HTTP service, years ago.

Hide these options from the server parameters, and replace them with
more appropriate 'http' ones:

 --xmlrpc-interface -> --http-interface
 --xmlrpc-port      -> --http-port
 --no-xmlrpc        -> --no-http

The config entries for these have been adapted as well.

The old parameter names are still silently supported in both
command-line arguments and config files. However they are
stored with the new names in the `tools.config` dict,
and when saving config files (with the -s option).

Also clarified and cleaned up the descriptions of the HTTP/WEB server
parameters.

And finally, added a short version `-p`, for the `--http-port` option.
Credits to @dreispt for this (via #19518)

Closes #19518
Closes #19778