[mqtt][homie] Implement non-retained and non-settable properties

[bodiroga]

This PR makes non-retained and non-settable properties usable, because right now they not fully supported as described in #8164.

With the proposed changes, this type of properties are modeled as state channels and as such are able to receive commands, but they don't update their states, as they are meant to be "stateless" (non-retained -> we don't want to store the value). That's why I have defined the VETO option for the AutoUpdatePolicy. At the same time, I have extended the generic Value class so that its children classes can implement the createCommandDescription() method. Usually this type of properties will be used with the "enum" data type, so providing a list of command options makes sense.

Feedback from @jochen314, @J-N-K, @cpmeister, @Hilbrand and @fwolter would be highly appreciated 😉

Closes #8164.

Signed-off-by: Aitor Iturrioz [email protected]

[TravisBuddy]

Travis tests were successful

Hey @bodiroga,
we found no major flaws with your code. Still you might want to look at this logfile, as we usually suggest some optional improvements.

[Hilbrand]

The code looks good to me. I have no idea if it's functionally correct though.

[bodiroga]

Hi @Hilbrand!

Many thanks for your review (and for the awesome job you are doing recently, you are on fire!). Just to help others understand what I have implemented in the PR, Homie properties can behave differently according to two important parameters: whether they are settable (true or false) and whether their values are retained (true or false). Thus we have four different combinations, as described here: https://homieiot.github.io/specification/#properties. The last one (non-retained and settable) was missing and requested by @ccutrer and that is what this PR tries to address, making the binding compatible with the four options.

If you have any question don't hesitate to ask, please, it would be great if this could be merged before the big OH3 refactory was done (@jochen314, @cpmeister, @J-N-K) 😉