Sensor name filtering

[oxplot]

Adds a new config option sensor_name_filter which is a regular expression. This is useful for when different types of sensors present different metrics under the same metric name.

[hikhvar]

I think this is a valid use case. However, this PR might not solve the problem. Given a mqtt metric state. Two types of sensors (a, b) use this name to represent different logical metrics state_a and state_b. With your implementation we can either filter for either a or b. The other state will be dropped. Is this intended?

[oxplot]

Is this intended?

No. And I see — the shape of the config file threw me off. I missed that a map is constructed to based on MQTT name.

I think the ingestor should iterate over all the rules and apply the first matching one.

[oxplot]

Done

[hikhvar]

LGTM. Thank you!