Add support for message decoding via Schema registry

[lasanthaS]

Purpose

This PR adds support to decode a protobuf messages via a schema registry.

Resolves wso2/streaming-integrator#242

Sample app as follows.

@App:name("protobuf")

@source(
    type='kafka',
    group.id = 'siddhiconsumer',
    is.synchronous='true',
    threading.option='single.thread',
    topic.list='StringsOnlyOptionOne',
    bootstrap.servers='localhost:9092',
    is.binary.message='true',
    optional.configuration="key.deserializer:org.apache.kafka.common.serialization.StringDeserializer,value.deserializer:io.confluent.kafka.serializers.protobuf.KafkaProtobufDeserializer,specific.protobuf.key.type:com.google.protobuf.GeneratedMessageV3,derive.type:false,schema.registry.url:http://localhost:8081",
    @map(type='protobuf', schema='registry',
        @attributes(a='Snack.colour', b='Snack.name')))
define stream LowProductionAlertStreamProtoBuf (a string, b string);

from LowProductionAlertStreamProtoBuf#log("Hit for protobuf2")
select *
insert into LogStream;

Security checks

• Followed secure coding standards in http://wso2.com/technical-reports/wso2-secure-engineering-guidelines? yes
• Ran FindSecurityBugs plugin and verified report? yes
• Confirmed that this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets? yes