Add stats for wasm remote load fetch and cache. (#515)
Add stats for wasm remote load fetch and cache. (#515)

(Backport from istio/envoy release-1.6)

Signed-off-by: John Plevyak <21e8c5cc24c747cac934fcbef39d1b757b61996c@gmail.com>
envoyproxy/envoy-wasm,envoyproxy/envoy-wasm,envoyproxy/envoy-wasm,envoyproxy/envoy-wasm,envoyproxy/envoy-wasm,envoyproxy/envoy-wasm,envoyproxy/envoy-wasm