Expose nats streaming sequence number as a transport property

[pcnfernando]

Purpose

Fixes #25

Approach

Expose nats streaming sequence number as a transport property

Sample

@source(type='nats', 
destination='SIDDHI_NATS_SOURCE_TEST_DEST', 
client.id='nats_client', 
bootstrap.servers='nats://localhost:4222', 
cluster.id='test-cluster, 
@map(type='json', @attributes(name='$.name', age='$.age', country='$.country', sequenceNum='trp:sequenceNumber')))
define stream inputStream (name string, age int, country string, sequenceNum string);