Add Dingtian DT-R002 relay board

[davidc]

Brief description of the changes

Add Dingtian DT-R002 relay board documentation.

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.

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[davidc]

I don't know why it thinks there are multiple H1s unless one is coming from the front matter, I did only use the generator on the esphome website though.

I'll fix the long lines.

[davidc]

I've removed the H1 since none of the other devices have one. I think the generator at https://devices.esphome.io/devices/adding-devices/#step-2-create-the-device-file needs fixing.