Update connector metadata schema with new features (#982)

- Change the nesting structure to more closely mimic how model types are
defined
- For instance, now all event datapoint level metadata are nested within
the event level metadata
- Re-shape destination fields to allow users to specify defaults
relevant to each supportable destination (default TTL/retain/qos/expiry
time on messages published for MQTT destination, default DSS key for
BrokerStateStore destination)
- Make connector metadata doc specify the min/max number of supported
events/datasets/streams/management groups/etc.
- Allow users to provide alternative names to our types like "event",
"datapoint", etc.
  - OPC UA refers to "datapoints" as "tags", for instance
- Disallow undefined fields from a connector metadata doc

Most of this is a breaking change, so it also bumps the version of the
connector metadata schema

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Co-authored-by: Raul Leclair <[email protected]>

Author: timtay-microsoft