sysutils/bacula15-server: Add support for zstd compression

You'll know you have zstd enabled if you find something like this:

$ ldd /usr/local/sbin/bextract | grep zstd
libzstd.so.1 => /usr/local/lib/libzstd.so.1 (0xbab736bf000)

$ ldd /usr/local/sbin/bacula-fd | grep std
libzstd.so.1 => /usr/local/lib/libzstd.so.1 (0x3e701988b000)

• add libzstd.so:archivers/zstd to LIB_DEPENDS
• apply upstream patches to configure and autoconf/configure

Those patches are:

• files/patch-configure https://gitlab.bacula.org/bacula-community-edition/bacula-community/-/commit/358e838a bring in some unset fixes, locally adjusted back to 15.0.2

• files/patch-autoconf_configure.in https://gitlab.bacula.org/bacula-community-edition/bacula-community/-/commit/8d9669fb fix detection of zstd

Upstream discussion: https://sourceforge.net/p/bacula/mailman/bacula-users/?viewmonth=202506

While here, comply with portlint for S3_LIB_DEPENDS

PR: 287403

Sponsored by: BSDCan 2025 FreeBSD Dev Summit

(cherry picked from commit 51b906b083febd50a4cfbb5e4278a59d95b50216)