Allow BigInt/Buffer to be used as initialSequenceId and/or sequenceId

[alanhoff]

Hello there,

Right now the producer's sequence ID is limited to 4 bytes here:

• https://github.com/apache/pulsar-client-node/blob/master/src/ProducerConfig.cc#L76
• https://github.com/apache/pulsar-client-node/blob/master/src/Message.cc#L174

However we could allow 8 bytes integers if we allow producer/message to receive a BigInt and/or a 8 bytes buffer.

I'm trying to match a dataset that uses 8 bytes integers for keys as my sequence ID, that's why I found this limitation :-)