Fix inconsistency in rate limit filter names

Minor cleanup related to PR #8796, for HTTP filters we have [`envoy.rate_limit`](https://github.com/envoyproxy/envoy/blob/master/source/extensions/filters/http/well_known_names.h#L39) but for networking filters we have [`envoy.ratelimit`](https://github.com/envoyproxy/envoy/blob/master/source/extensions/filters/network/well_known_names.h#L27). We should update the network filter to match HTTP/Thrift. In order to avoid naming collisions, the network filter should be updated to the new style of `envoy.filters.network.rate_limit`. This would involve
1. [Register a second definition](https://github.com/envoyproxy/envoy/blob/master/source/extensions/filters/network/ratelimit/config.cc#L44) of the rate limit filter's [config factory](https://github.com/envoyproxy/envoy/blob/master/source/extensions/filters/network/ratelimit/config.h#L18) with the [new name](https://github.com/envoyproxy/envoy/blob/master/source/extensions/filters/network/ratelimit/config.h#L21).
2. Deprecation period for the old config factory
3. Removal of the old config factory

(while here, we could extend this to updating all the networking filter names to the new format, this one just stood out as a potential nuisance)