Feature: Make sure that MQTT LWT is well authroized

[drasko]

Is your feature request related to a problem? Please describe.

Maybe - it might be that LWT is not well authorized currently, and that the broker will shoot it to topics it should not, as it sends it on behalf of a certain client (wich might not have permissions to publish on that topic).

Describe the feature you are requesting, as well as the possible use case(s) for it.

Forllowing this and this, we must make sure that LWT topic in CONNECT package is valid, i.e. that client has permissions to publish on that topic.

One trouble with that is that permissions to publish on that topic might change during the life of the client, but the LWT config stays written in the broker and will be executed upon the client disconnection. We need to agree how we will treat this case - probably for now best we can do is just allow if on connection this is allowed, or force re-connect upon changed permissions, if the changed permissions were on client's LWT topic (LWT topic is important and should be also shown in UI).

Indicate the importance of this feature to you.

Must-have

Anything else?

No response