Generate ATS 2.0 config for Mobly test.

- Support test_config and test_config_template
- The `config` file extension is widly used by TF. Use `configv2` for
  ATS 2.0 tests to avoid configuration errors in TF.
- Add `mobly` tag to support atest

Test: m CtsBluetoothMultiDevicesTestCases (with `runner = "mobly"`)
Bug: 299850687
Change-Id: Idbed90ab30e35aeed8cdeeb0aa0aa7adb75a3cd9