Bug 18137: Migrate from Swagger2 to Mojolicious::Plugin::OpenAPI

Bug 18137: Migrate from Swagger2 to Mojolicious::Plugin::OpenAPI

This patch migrates from Swagger2 to Mojolicious::Plugin::OpenAPI as Swagger2 is
no longer actively maintained.

This migration involves some minor changes to our Swagger specification documents
and to controllers. Each operation is migrated in following patches separately.
Please see Mojolicious::Plugin::OpenAPI and its tutorial for more documentation.

The patch also refactors some API authentication -related code by taking advantage
of Koha::Exceptions. Authentication is now handled via Mojolicious's "under->to"
functionality. The actual authentication & authorization checks are moved to
Koha::REST::V1::Auth. Added a HTTP 503 response for when database update is
required, instead of returning an authentication failure as before.

To test:
1. prove t/db_dependent/api/v1/auth.t

Signed-off-by: Olli-Antti Kivilahti <olli-antti.kivilahti@jns.fi>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>