Add Heltec LoRa 32 V3 docs

[swoboda1337]

Brief description of the changes

Add heltec v3 docs

Type of changes

• [x] New device
• [ ] Update existing device
• [ ] Removing a device
• [ ] General cleanup
• [ ] Other

Checklist:

• [x] There are no passwords or secrets references in any examples. The only exceptions are !secret wifi_ssid and !secret wifi_password.
• [x] The wifi or ethernet block has no static / manual ip address specified.
• [x] 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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