Add system message(s) support

[SphtKr]

What I would like to do here is somehow support multiple system messages in a better way than the HA integration does (it keeps switching the message back and forth if there are two). Probably this will be "System Message N" where "N" is 1, 2, 3 ... many questions remain here though.

Is there a maximum? Should all be registered initially? Or should additional ones be added to discovery as they occur? Configure via options? And how to manage their ordering? The goal would be to keep them from "flapping" as much as possible, so somehow we will have to "guess" when one has been cleared, and... then what?

E.g., if there is a "Low Salt" in position 1 and a "Check Cell" message in position 2, and the "Low Salt" condition is cleared, then,

1. When is the "Low Salt" message considered gone? After a certain time without being seen, or when "Check Cell" cycles back N times without seeing "Low Salt"?
2. Does "Check Cell" become the message in "System Message 1" or remain in "System Message 2" until it is cleared?

Alternatively, should all known system messages just be published as binary_sensor? Is there a known list somewhere?