Bug 21403: Add Indian Amazon Affiliate option to AmazonLocale setting

Bug 21403: Add Indian Amazon Affiliate option to AmazonLocale setting

This patch adds an "IN" option to the AmazonLocale setting, allowing
Indian libraries to use their Amazon Affiliate ID in Koha's links to
Amazon.

To test, apply the patch and run updatedatabase.

- Go to Administration -> System preferences -> Enhanced content.
- Enable the OPACAmazonCoverImages preference.
- Enter a dummy ID in the AmazonAssocTag preference.
- Confirm that you can select "Indian" for the AmazonLocale preference.
- Select "Indian" and save.
- Open a record in the OPAC and confirm that the cover image links to
  Amazon.in and includes the ID you entered in AmazonAssocTag.
- Do the same with a record in the staff client.

Signed-off-by: Pierre-Marc Thibault <pierre-marc.thibault@inLibro.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>