Bug 28340: Alphabetise metadata for notices

Bug 28340: Alphabetise metadata for notices

This commit sorts metadata by key prior to preparing a notice with it

Test plan:

- Do not apply patch
- Create a report with the following SQL:
  SELECT * FROM message_queue;
- Create an ILL request with plenty of metadata
- Go to "Manage request"
- Send a notice to a patron
- Run the report created earlier

=> TEST:
- Observe that the metadata is in random order

- Apply the patch
- Create an ILL request with plenty of metadata
- Go to "Manage request"
- Send a notice to a patron
- Run the report created earlier

=> TEST:
- Observe that the metadata is now sorted alphabetically by key

Signed-off-by: Jill Tivey <Jill.Tivey@sasa.gov.scot>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>