Bug 23666: Add PATCH /patron/:patron_id/extended_attributes/:extended_attribute_id

Bug 23666: Add PATCH /patron/:patron_id/extended_attributes/:extended_attribute_id

This patch adds the described route. It is designed to use the
underlying libraries' methods to update an existing attribute.

The tests cover the use cases.

Note: I added handling for two exceptions that can only occur on bad
data (i.e. not by using our codebase). This are:
- Koha::Exceptions::Patron::Attribute::InvalidType
- Koha::Exceptions::Patron::Attribute::NonRepeatable

To test:
1. Apply this patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/api/v1/patrons_extended_attributes.t
=> SUCCESS: Tests pass!
3. PLay with the route
=> SUCCESS: Expected behavior!
4. Sign off :-D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>