update jwt filter sample envoy.conf to align with latest config proto (#1403)
update jwt filter sample envoy.conf to align with latest config proto (#1403)

Automatic merge from submit-queue.

Update jwt filter sample envoy.conf to align with latest config proto

**What this PR does / why we need it**:
Update jwt filter sample envoy.conf to align with latest config proto

**Which issue this PR fixes** 
try sample in https://github.com/istio/proxy/blob/master/src/envoy/http/jwt_auth/README.md, it fails 

bazel-bin/src/envoy/envoy -c src/envoy/http/jwt_auth/sample/envoy.conf
hit error initializing configuration 'src/envoy/http/jwt_auth/sample/envoy.conf': Unable to parse JSON as proto (INVALID_ARGUMENT:: Cannot find field.): {"jwts":[{"jwks_uri_envoy_cluster":"example_issuer","jwks_uri":"http://localhost:8081/","issuer":"628645741881-noabiu23f5a8m8ovd8ucv698lj78vv0l@developer.gserviceaccount.com"}]}


**Special notes for your reviewer**:

**Release note**:
istio/proxy,lizan/proxy,istio/proxy,lizan/proxy,lizan/proxy,istio/proxy,lizan/proxy,istio/proxy