Title: Similarly to HTTP use case, add injectDataToFilterChain(data, end_stream) methods to NetworkFilter callbacks

Description:

Recently, new methods have been added to StreamFilterCallbacks in order to support low bandwidth simulation (see #6242):

• StreamDecoderFilterCallbacks::injectDecodedDataToFilterChain(data, end_stream)
• StreamEncoderFilterCallbacks::injectEncodedDataToFilterChain(data, end_stream)

It would be useful to have methods with the same semantics in the context of NetworkFilters as well.

Example use cases include:

• low bandwidth simulation at L4 (see Slow network / local rate limit HTTP filter #5942)
• piping request/response data through an out-of-process filter (see Add ability to execute Filters over gRPC to mutate payload. #5209)