www/bacula-web: Fix installation for complete freshly installed FreeBSD

If you install bacula-web without any special options set
it is using by standard sqlite3 for the database.

But this is not available with the standard options defined.
Install by default all 3 options (mysql, pgsql, sqlite).
The user can remove database support if required by compiling the
package with required options set.

But we should not block users using pkg to install the package
by using another database then pgsql.