[Bug] OTEL push method is stored as a database method

Start with buildPropertiesFromGrpc() in pkg/util/parse and trace the OTEL branch alongside the HTTP and MQTT branches. Run go test -mod=mod ./pkg/util/parse and use the focused regression test to verify that an OTEL property sets PushMethod.MethodName to common.PushMethodOTEL and is initialized by the OTEL handler.

What happened:

buildPropertiesFromGrpc() assigns the OTEL push method constant to DBMethodName instead of PushMethod.MethodName. The generated mapper therefore does not recognize the property as an OTEL push method.

What you expected to happen:

A device property configured with an OTEL push method should produce PushMethod.MethodName == common.PushMethodOTEL and be initialized by the OTEL handler.

How to reproduce it:

1. Build a DMI device with one property whose PushMethod.Otel is set.
2. Pass the device to buildPropertiesFromGrpc().
3. Inspect the resulting DeviceProperty.PushMethod.
4. The current code leaves MethodName empty and writes otel into DBMethodName instead.

Proposed fix:

Store common.PushMethodOTEL in pushMethodName, matching the HTTP and MQTT branches. A focused regression test covers the parser output.

Validation:

go test -mod=mod ./pkg/util/parse passes with the repository API dependency on macOS.