Update ISY994 documentation to be model agnostic

[shbatm]

Proposed change

Revises the isy994 integration to be more agnostic to specific UDI model numbers. The "ISY" term is now more broadly associated with Universal Devices' software rather than the legacy ISY994 device. They have also introduced the IoX term to refer to ISY-on-Anything firmware, which runs the control software on their newer Polisy and eisy devices.

1. Change Title from "Universal Devices ISY994" to "Universal Devices ISY/IoX" to reflect new UDI naming.
2. Generalize "ISY994" to "ISY" where referring to the software and not the specific model number.

At this point, I don't believe it's worth the hassle of changing the integration domain from isy994, simply to avoid breaking changes, but this will help users understand that the integration is for the full ISY family, not just the ISY994 device.

Type of change

• Spelling, grammar or other readability improvements (current branch).
• Adjusted missing or incorrect information in the current documentation (current branch).
• Added documentation for a new integration I'm adding to Home Assistant (next branch).
  • I've opened up a PR to add logo's and icons in Brands repository.
• Added documentation for a new feature I'm adding to Home Assistant (next branch).
• Removed stale or deprecated documentation.

Additional information

• Link to parent pull request in the codebase: Update ISY994 integration to be model agnostic core#85017
• Link to parent pull request in the Brands repository: n/a
• This PR fixes or closes issue: fixes # n/a

Checklist

• This PR uses the correct branch, based on one of the following:
  • I made a change to the existing documentation and used the current branch.
  • I made a change that is related to an upcoming version of Home Assistant and used the next branch.
• The documentation follows the Home Assistant documentation standards.

[home-assistant]

It seems that this PR is targeted against an incorrect branch. Documentation updates which apply to our current stable release should target the current branch. Please change the target branch of this PR to current and rebase if needed. If this is documentation for a new feature, please add a link to that PR in your description.

[frenck]

Thanks, @shbatm 👍

Happy New Year 🥂

../Frenck