[Feature] Improved Status Endpoint

#### What problem would the feature you're requesting solve? Please describe.
A single place to go to understand the health of my function app (and all functions within it). Potential scenarios include: alerting customers when something about their system has become unhealthy, building automation to rollback deployment if an app becomes unhealthy, displaying in the Azure portal what the overall status of a function app is

#### Describe the solution you'd like
Probably an ARM API? But that's up to dev :)

#### Describe alternatives you've considered
The host status endpoint isn't sufficient here - it gives basic information about the current status of the host, but we need more. Also, if the host is unavailable, sometimes this API is too, which gives us very little information.

#### Additional context
The portal will benefit from this massively, but there are other reasons to do it as well!