RTL872x: Implement APIs to set/get BLE address

[XuGuohui]

As the title describes.

Example App

void setup() {
    BLE.on();
    BLE.advertise();
    // BLE.setAddress("D3:12:34:56:78:AB");
    delay(3000);
    auto foo = BLE.address();
    Log.info(foo.toString());
}

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Completeness

• User is totes amazing for contributing!
• Contributor has signed CLA (Info here)
• Problem and Solution clearly stated
• Run unit/integration/application tests on device
• Added documentation
• Added to CHANGELOG.md after merging (add links to docs and issues)