Bug 29810: Add 'x-koha-embed' to reserved words

Bug 29810: Add 'x-koha-embed' to reserved words

The maintainers of Mojolicious::Plugin::OpenAPI and friends fixed the
problem with using collectionFormat for Headers in the upstream library.

However, this highlighted an outstanding issue in our code when I ran
the unit tests. We have not been stripping x-koha-embed at the query
level as it did not exist in the reserved_words list.  This patch
resolves that and gets the acquisitions_orders test passing again.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>