Bug 37157: Fix Malformed UTF-8 character in JSON string before decode_json

Bug 37157: Fix Malformed UTF-8 character in JSON string before decode_json

When we add a new identity provider and put some special characters in the Config or Mapping field, we got 500 error when we list the identity providers

To test:
1. Apply this patch.
2. Add a new identity provider
    2.1. fill the form
    2.2. click on «Add default Oauth configuration» and on «Add default Oauth mapping»
    2.3. put some special characters in Configuration and Mapping field
3. Save the form
=> Confirm the identity providers list is shown correctly

Also prove t/db_dependent/api/v1/provider.t.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>