Bug 26947: Add schema-only option to koha-dump

Bug 26947: Add schema-only option to koha-dump

This patch adds a new --schema-only optoin to the koha-dump script.

This can be used to generate a new kohastructure.sql file during the release, and later to
compare the DB structure of a koha instance to the kohastructure.sql file shipped with a version
to identify any missing constraints or other db structure issues

To test:
1 - debian/scripts/koha-dump kohadev
2 - Confirm db and configs are dumped correctly
3 - Apply patch
4 - debian/scripts/koha-dump --help
5 - Confirm new option is listed and makes sense
6 - debian/scripts/koha-dump --schema-only kohadev
7 - Confirm only schema is dumped and is not zipped
8 - debian/scripts/koha-dump kohadev
9 - Confirm entire db is dumped as before

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>