Kafka Source default value for max_partition_fetch_bytes too high

[hrabalp]

BitSwanPump/bspump/kafka/source.py

Line 38 in 52ee17b

'max_partition_fetch_bytes': 1048576,

When there is more complex (slow ) processing in the pipeline it may timeout from kafka side and sourcre crashes (first commit gets error, retry fail as well)
Default value should be significantly more defensive (10% of current?)

User can allways incerease this value if he feels its required

[SukiCZ]

The value is the same as default in aiokafka/consumer