"ensure value" endpoint

[bentheiii]

add a new endpoint that will ensure that the value in a certain partial context will be equal to a certain value, this endpoint should either create a new rule or modify an existing one, this endpoint should have two modes:

• force=False: in this mode, if there are multiple rules for a sub-context (i.e. adding or modifying one rule will not guarantee the value at all sub-contexts of the partial context), an error will returned
• force=True: in this mode, all rules for sub-contexts will be deleted

possible routes:

• PUT api/v1/setting/<id>/value