telemetry client updated to stream structured events

[renukamanavalan]

Why I did it

Refer: https://github.com/sonic-net/SONiC/pull/954 NOTE: Dependent on PR #649 and update of swss-common in buildimage.

How I did it

Added a new client with APIs from libswsscommon to receive events.

How to verify it

After buildimage PR too checked in for this feature, toggle BGP states and note events streaming out. gnmi_cli -client_types=gnmi -a 127.0.0.1:50051 -t EVENTS -logtostderr -insecure -v 7 -streaming_type ON_CHANGE -q aaa/bbb -qt s

Which release branch to backport (provide reason below if selected)

• [ ] 201811
• [ ] 201911
• [ ] 202006
• [ ] 202012
• [ ] 202106
• [ ] 202111

Description for the changelog

Link to config_db schema for YANG module changes

A picture of a cute animal (not mandatory but encouraged)

[lgtm-com[bot]]

This pull request introduces 1 alert when merging 8e243a209bfcbb151aad8d18444fbbc8ba11e29c into 1ac0e0e2170dc6d928818a5d7e69aba248dd0f6e - view on LGTM.com

new alerts:

• 1 for Unreachable statement

[renukamanavalan]

@yozhao101, @abdosi, @zbud-msft, @qiluo-msft,

Can you please provide your reviews, ASAP ? We are currently blocked. This will help us progress.

[abdosi]

can we please add some UT here ?

[renukamanavalan]

can we please add some UT here ?

Yes we do. Currently there are no unit tests for any sonic-data client. This would be a bigger task, so we will add it as a work item and get to it.

@abdosi , can you please comment/approve?