Add Availability to UI templates

[epenet]

When templates were added to the UI, Availability was apparently purposefully left out:

The core team decided it was OK to bring template helpers to the UI, but in a limited way. Some of the goals taken into account were: Prevent the UI from becoming overwhelming for users with all kinds of experience levels, and preventing from ending up with a lot of options in a configuration flow that hurts UX.
Therefore, we added the bare minimum fields that will satisfy a guesstimate of 80-90% of the use cases. With YAML support still being available, all other use cases would still be possible.

I propose that Availability is added to the UI for at least some UI templates

Sample PRs:

• sensor in Add Availability to sensor template config flow core#126806
• binary_sensor in Add Availability to binary sensor template config flow core#126807

Related to https://community.home-assistant.io/t/add-availability-template-to-the-new-template-sensor-helper/621069
See also #1148

[frenck]

Seems like we crossed paths there.

But as per home-assistant/core#126806 (comment), this proposal has been decided against.

../Frenck

[epenet]

Adding the full clarification here for reference:

Small clarification.

Bringing templates to the UI was quite a long discussion. The core team decided it was OK to bring template helpers to the UI, but in a limited way. Some of the goals taken into account were: Prevent the UI from becoming overwhelming for users with all kinds of experience levels, and preventing from ending up with a lot of options in a configuration flow that hurts UX.

Therefore, we added the bare minimum fields that will satisfy a guesstimate of 80-90% of the use cases. With YAML support still being available, all other use cases would still be possible.

Adding this, breaks with the decisions made at the time. I'm adding this PR to to core team meeting agenda to discuss.

../Frenck