Added device Mill panel heater generation 2

[owangen]

Brief description of the changes

Added new device Mill panel heater to enable it to be controlled by esphome. Based on earlier work that was a custom component.

Type of changes

• New device
• Update existing device
• Removing a device
• General cleanup
• Other

Checklist:

• There are no passwords or secrets references in any examples.
  The only exceptions are !secret wifi_ssid and !secret wifi_password.
• The wifi or ethernet block has no static / manual ip address specified.
• The first configuration provided should be hardware definitions only.
  A more involved example can be provided in a separate configuration block.

[netlify]

✅ Deploy Preview for esphome-devices ready!

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🔨 Latest commit	76c3458
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Lighthouse	1 paths audited Performance: 97 (🟢 up 4 from production) Accessibility: 86 (no change from production) Best Practices: 100 (no change from production) SEO: 89 (no change from production) PWA: 70 (no change from production) View the detailed breakdown and full score reports

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