[web] add client interceptors for grpc-web

Summary:
these interceptors will be used to add version and auth metadata to our RPCs.

Depends on D9671

Test Plan: https://gist.github.com/vdhanan/15ffc5810425b8a22b7d3c5bd01a8d58

Reviewers: ashoat

Reviewed By: ashoat

Subscribers: bartek, tomek, wyilio

Differential Revision: https://phab.comm.dev/D9672