Allow multiple local rate limit configurations per route or virtual host

Title: Allow setting multiple local rate limit configurations per route or virtual host

Description: It is useful to define rate limits for a few resolutions, for instance 50 requests/second and 1000 requests/minute for the same route or virtual host.

The global rate limiting API allows multiple rate limit configurations per route or virtual host.

The local rate limiting API, however, only allows a single local rate limits configuration.

Using Istio 1.8.1 + Envoy 1.16.1, I am only able to effectively define one local rate limit configuration per route or virtual host. Since I need to define two local rate limit resolutions, I am going around this limitation by defining one token bucket configuration for the inbound virtual host, e.g. 50 requests/second, and another token bucket configuration for the outbound virtual host, e.g 1000 requests/second. If I needed to set up more than two local rate limit resolutions, I wouldn't be able to.