[pdata] Allow strict enforcement of json payloads.

[TylerHelmuth]

Is your feature request related to a problem? Please describe.
To enable the collector to receive json payloads from new/old otel exports, the collector was changed to skip unknown fields instead of error (#5312, #5931). This is a proper default behavior, but there may be situations where users rely on the collector strictly enforcing json payload structure. It would be nice if the collector provided the option to enable strict enforcement of json payloads.

Describe the solution you'd like
Maybe a startup option for the collector? Or something in the collector config's service section.

Describe alternatives you've considered
Pushing responsibility to receivers. This is possible, but would require individual receivers to make changes/choices, versus the collector enforcing the structure for all incoming data.