Add support of Traffic-routing spec

[123liuziming]

Describe what this PR does / why we need it

Does this pull request fix one issue?

refrence to issue 16

Describe how you did it

Add xds proto so that OpenSergo can listen the route configuration

Describe how to verify it

Special notes for reviews

[123liuziming]

and the traffic-routing proto files of opensergo should be added into directory src/main/proto/ Therer is no traffic-routing proto, we just reuse the proto in xds

[sczyh30]

and the traffic-routing proto files of opensergo should be added into directory src/main/proto/

Actually we just leveraged the original "route configuration" from xDS RDS proto (and there are some extension fields inside it, which may satisfy our requirement)

[sczyh30]

cc @123liuziming @panxiaojun233 We may need to add some description for our design later.

[jnan806]

cc @sczyh30 @123liuziming @panxiaojun233 I will merge it with squash and merge

[sczyh30]

Nice work. Thanks!