History-graph: do not make a graph for "unavailable" sensor transparent

[ildar170975]

Checklist

• [X] I have updated to the latest available Home Assistant version.
• [X] I have cleared the cache of my browser.
• [X] I have tried a different browser to see if it is related to my browser.

Describe the issue you are experiencing

Since 2022.12.4 a graph for "unavailable" entity is shown of transparent color.

This is confusing:

1. No graph for some entity may be considered as bug.
2. Transparent color = gap, but currently a gap is displayed in cases when an entity does not exist.

And when within the selected period the entity is unavailable - then no graph is displayed at all: which is super-confusing.

Describe the behavior you expected

Graph for "unavailable" sensor must not be transparent. Better to use some theme variable like --history-state-color-unavalailable.

Steps to reproduce the issue

as above

What version of Home Assistant Core has the issue?

2022.12.4

What was the last working version of Home Assistant Core?

No response

In which browser are you experiencing the issue with?

Chrome 108.0.5359.99

Which operating system are you using to run this browser?

Win10x64

State of relevant entities

No response

Problem-relevant frontend configuration

No response

Javascript errors shown in your browser console/inspector

No response

Additional information

No response