Adds MockJoinGroupResponse, MockLeaveGroupResponse, MockSyncGroupResponse, MockHeartbeatResponse for mocking consumer groups
Adds MockJoinGroupResponse, MockLeaveGroupResponse, MockSyncGroupResponse, MockHeartbeatResponse for mocking consumer groups

Squashed commit of the following:

commit d80a202edf65301c47af457b44043e3fedd54efd
Merge: 6dbd2ce 65f0fec
Author: Kranti Deep <kranti.deep@razorpay.com>
Date:   Sun Oct 11 22:37:51 2020 +0530

    Merge branch 'master' into cd/1577/consumer-group-mocks

commit 6dbd2ce4ce7d3222cb5126d32b40ff07260c30c5
Merge: 94dce3e c1c2a08
Author: Kranti Deep <kranti.deep@razorpay.com>
Date:   Wed Aug 12 20:46:55 2020 +0530

    Merge branch 'master' into cd/1577/consumer-group-mocks

commit 94dce3e27b076b2c2be44c8dd1ee8c10219293af
Author: Kranti Deep <kranti.deep@razorpay.com>
Date:   Sun Jul 12 23:05:21 2020 +0530

    change return type of MockJoinGroupResponse.For, MockHeartbeatResponse.For & MockLeaveGroupResponse.For to encoderWithHeader

commit ac5ca79bb834918ddff9c8baf841eda6624fa4d8
Merge: e81f001 5933302
Author: Kranti Deep <kranti.deep@razorpay.com>
Date:   Sun Jul 12 22:52:16 2020 +0530

    Merge branch 'master' into cd/1577/consumer-group-mocks

commit e81f001564409e2ccfc3653aafe81c28ee12e2ac
Author: Carl Dunham <cdunham@gmail.com>
Date:   Tue Feb 25 16:40:16 2020 -0500

    add basic mocks for consumer group responses

DataDog/sarama,Shopify/sarama,Shopify/sarama,DataDog/sarama