Add retry for rooftop sites collection #12

[autoSteve]

What I think is going on with #12 is that 'random' 429 errors from Solcast (i.e. "Back off, we're busy!") prevent the integration from loading properly on startup. This causes sensors to go missing, which is sub-optimal.

Caching rooftop sites is one option, and I like it, but that carries real-world use case implications (add array? delete array? modify array? rename array?). There would have to be an easy and intuitive way to force refresh the cache, which is unlikely. Or a once-a-day attempt at refreshing the cache.

Another option is simply retrying until the data can be had.

This marge attempts a retry approach, where for up to one minute it will try every six seconds.

It's going to be very difficult to test this, because how can you guarantee Solcast will be busy on any given hour/minute/week/etc. and return a 429? And the only real way of testing is repeatedly restarting HA so that the integration loads the rooftop sites, which it only does on startup.

[BJReplay]

A well thought out approach. I agree - I don't see how this is easy to test (at least not without a MITM proxy).