Bug 37856: Add service_platform field

Bug 37856: Add service_platform field

The change from this patch itself should be self-explanatory.
Testing for this requires credentials to a specific provider.
But the parameter is only added to the URL if defined.

Test plan, ktd, apply patch, run:
$ yarn js:build
$ yarn api:bundle
$ koha-plack --restart kohadev

1) Enable ERMModule
2) Create a new provider, visit:
<staff_url>/cgi-bin/koha/erm/eusage/usage_data_providers/add
3) Ensure 'Service platform' now shows. Create the provider and put something in this field.
4) View the provider, ensure the field is shown, visit:
<staff_url>/cgi-bin/koha/erm/eusage/usage_data_providers/1

Ensure all tests are still passing:
$ cypress run --spec t/cypress/integration/ERM/DataProviders_spec.ts
$ prove t/db_dependent/api/v1/erm_usage_*

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