http cache filter says it will wait until the cache implementation returns ready, but doesn't wait

*Title*: http cache filter suggests it will wait until the cache implementation returns ready, but doesn't wait

*Description*:
>With an asynchronous cache implementation, if many items are requested at once, and the network is fast, the cache filter slams all the data into the cache implementation all at once, and the cache has no way of saying "woah, slow down, this hasn't been processed yet". The data therefore ends up all crammed into memory buffers, not the usual stream buffer with the watermarks, easily provoking an OOM problem.
>
>Suggestion that it will wait is [here](https://sourcegraph.com/github.com/envoyproxy/envoy/-/blob/source/extensions/filters/http/cache/http_cache.h?L143-146)
>
>Implementation that doesn't wait is [here](https://sourcegraph.com/github.com/envoyproxy/envoy/-/blob/source/extensions/filters/http/cache/cache_filter.cc?L170-172)