libpq_pipeline: Must strdup(optarg) to avoid crash

libpq_pipeline: Must strdup(optarg) to avoid crash

I forgot to strdup() when processing argv[].  Apparently many platforms
hide this mistake from users, but in those that don't you may get a
program crash.  Repair.

Per buildfarm member drongo, which is the only one in all the buildfarm
manifesting a problem here.

While at it, move "numrows" processing out of the line of special cases,
and make it getopt's -r instead.  (A similar thing could be done to
'conninfo', but current use of the program doesn't warrant spending time
on that -- nowhere else we use conninfo in so simplistic a manner.)

Discussion: https://postgr.es/m/20210401124850.GA19247@alvherre.pgsql