OTLP Exporter: allow json export

[xuan-cao-swi]

OTLP Specification 1.7.0

Telemetry data is sent via HTTP POST request. The body of the POST request is a payload either in binary-encoded Protobuf format or in JSON-encoded Protobuf format.

Java implementation: https://github.com/open-telemetry/opentelemetry-java/blob/main/exporters/common/src/main/java/io/opentelemetry/exporter/internal/http/HttpExporterBuilder.java#L172

[github-actions]

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