Allow to set success_before_passing and failures_before_critical via agent endpoint

[onimsha]

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Feature Description

Consul Agent Endpoint /v1/check/register and /v1/service/register should accept success_before_passing and failures_before_critical in the payload. Right now (consul 1.7.2) it returns HTTP 400 and does not recognise these fields.

Use Case(s)

With system that relies on the agent endpoint to register services & checks on startup and doesn't want to use a configuration file on the agent side, this feature is really a big help.

For example our system is using a discovery process, when the application is doing some preparation, gather host's information before sending the request to consul agent for service registration.