Add addon availability API

[mdegat01]

Proposed Changes

Add support for the addon availability API added in home-assistant/supervisor#6140

[agners]

The key pretty much should be enough identifying information to derive the message from. I wonder if we should have made the message_template just a local, static field of the exception and not transmitted over the wire 🤔 .

Anyhow, it can come in handy to make small adjustments/improvements, and probably doesn't matter much that we transmit it over the wire.

[mdegat01]

@agners yea I agree. For some reason I thought I'd be reconstituting the message using the message template in the client library, that was why I added it. Then when doing the code here I realized that didn't make sense, I already had the message. Maybe I should drop the field from the client library for now? It already made the API but that doesn't mean it has to be added here if we don't need it.

[agners]

For some reason I thought I'd be reconstituting the message using the message template in the client library, that was why I added it.

You ended up using the template from what I can tell no? The message template is only in the fixtures, which tries to reflect what Supervisor returns.

Having the message template string on server side has the benefit that we can alter it. On the other hand it makes things more difficult for translations: Translators need to check Supervisor code to find the English original template 🤔 .

[agners]

This now aligns with latest Supervisor change where we removed message_template again (see home-assistant/supervisor#6205).

LGTM!