Bug 21116: Unit tests

Bug 21116: Unit tests

This path implements unit tests for the route-from-plugin development.
It adds the required methods to the Koha::Plugin::Test plugin
distributed along with the tests. A second plugin implementing invalid
OpenAPI specs is added (Koha::Plugin::BadAPIRoute).

Edit: I made terminology changes to make it less rude.

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Alex Arnaud <alex.arnaud@biblibre.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
(cherry picked from commit 46c992948ea28ae2bebc7f9042df6434319b80bf)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>