Address potential unhandled exceptions in OTLP exporters

Is your feature request related to a problem?

Under scenarios when invalid signal-specific objects as passed to OTLP exporters, an unhandled exception can be thrown which directly violates the requirements outlined by the spec: https://opentelemetry.io/docs/specs/otel/error-handling/

OpenTelemetry implementations MUST NOT throw unhandled exceptions at run time.

Two ways in which this issue can be addressed are:

1. Update encode_metrics/encode_traces/encode_logs to NOT raise an exception, and instead log an error when unexpected data is encountered
2. Update OLTP metric exporters to handle the exception, logging the error and returning an export failure result

For additional context see #4996.

Would you like to implement a fix?

Yes

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