Calculate Physical Input size for query stats in Mongo DB connector

[krvikash]

Mongo DB connector does not calculate physical input size and always returns 0.

trino/plugin/trino-mongodb/src/main/java/io/trino/plugin/mongodb/MongoPageSource.java

Lines 113 to 117 in a0eb0a1

	@Override
	public long getCompletedBytes()
	{
	return 0;
	}

This Physical Input size will be helpful for adding a test case for dereference pushdown (#17710) comparing physical input size with and without enabling dereference pushdown.