doc: add Jinja2 requirement for protodoc target (#15623)
doc: add Jinja2 requirement for protodoc target (#15623)

Signed-off-by: Takeshi Yoneda <72d3043deb9ea484d21ffcca03f662fa81cbe321@tetrate.io>
lyft/envoy,envoyproxy/envoy,lyft/envoy,lyft/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,lyft/envoy,lyft/envoy,lyft/envoy,envoyproxy/envoy