Solcast cloud service support, documentation updates

What's Changed

Added support for Predbat to talk directly to Solcast

You can now set your API key for Solcast in apps.yaml and have Predbat talk directly instead of using the Solcast plugin as follows:

  # Solcast cloud interface, set this or the local interface below
  solcast_host: 'https://api.solcast.com.au/'
  solcast_api_key: 'xxxx'
  solcast_poll_hours: 8

Keep in mind that if you have Predbat connected to Solcast it will use up your maximum polls per day so its best to pick either Predbat direct or Solcast integration but not both.

• Solcast integration by @springfall2008 in #1154
  • Solcast updates, error logging by @springfall2008 in #1156

Documentation updates

Updated the Predbat documentation to include the Predbat add-on and Sunsynk inverters
Added Solcast configuration via Predbat

• Documentation updates for Predbat add-on, Solcast and Sunsynk by @springfall2008 in #1157

Full Changelog: v7.20.6...v7.21.0