Bug 27797: Make POST /holds use the stashed koha.overrides

Bug 27797: Make POST /holds use the stashed koha.overrides

Bug 26181 introduced a way to override behavior through a new header,
x-koha-override. And bug 27760 introduced a generic approach to handle
x-koha-override.

This patchset makes the POST /api/v1/holds route rely on this new way of
handling x-koha-override instead of doing it manually.

The header is added to the spec as a parameter.

Note: the header should be defined as:

    "type": "array",
    "collectionFormat": "csv",
    "items": {
        "type": "string",
        "enum": [
            "any"
        ]
    }

but the versions of JSON::Validator we use have lots of bugs related to
header type coercion, so it just doesn't work. The changelog for
JSON::Validator is fairly elocuent about it.

The override now takes a list of valid keywords (right now only 'any'
but it would be fairly straight-forward to add a fairly granular set of
options based on each possible AddReserve failure.

To test:
1. Apply this patches
2. Run:
   $ kshell
  k$ prove t/db_dependent/api/v1/holds.t
=> SUCCESS: Tests pass!
4. Sign off!

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>