esim/http_json_api: add alternative API interface (follow up)
This is a follow up patch to change:
I2a5d4b59b12e08d5eae7a1215814d3a69c8921f6
- do not ignore length of kwargs
- fix role parameter (roles other than 'legacy_client' can be used now)
- use startswith instead of match
Related: SYS#7866
Change-Id: Ifae13e82d671ff09bddf771f063a388d2ab283eb
