Add PostgreSQL home page to --help output

Example:

initdb --help
...
Report bugs to <pgsql-bugs(at)lists(dot)postgresql(dot)org>.
PostgreSQL home page: <https://www.postgresql.org/>

I think this is useful. You see this nowadays in other packages as
well. See also
<https://www.gnu.org/prep/standards/standards.html#g_t_002d_002dhelp>
for a reference.

Autoconf already has a way to register the package home page and
propagate it, so I used that. That also makes it easier to change it
(see http: -> https:) or have third parties substitute their own contact
information without destroying translations.

While at it, I also did the same refactoring for the bug reporting
address (which was also recently changed, so this is a bit late, but who
knows what the future holds).

--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services