WASM runtime telemetry

*Description*:
Currently there is not possible to alert on (WASM) extension failure.
It would be very desirable to to allow monitoring of WASM extensions, particularly failing in `fail_open` state.
(it would be nice to have _fail close_ as well; while that's inferable from no traffic, it would help faster diagnostics)

it would also be helpful to have indication of how many distinct filters are applied if practical (as I understand, currently there is a wasm runtime per worker thread and possibly per listener or filter chain, so it makes it difficult to observe if my extensions are applied as expected)

[optional *Relevant Links*:]
currently there is no stats regarding health of an extension
https://www.envoyproxy.io/docs/envoy/latest/configuration/other_features/wasm

cc: @PiotrSikora