Allow setting a destination for log messages from wasm plugins

Title: Allow setting a destination for log messages from wasm plugins

Description:

Currently, logging from wasm plugins all go to envoy's app logs. However, there are use cases for separating out log files for specific domains - for example, a WAF filter will often need to have a separate audit log which is used for actioning on suspicious events.

One approach could be for the config to define log destinations

message LogDestination {
  oneof {
    string file_path = 1;
    
    string remote_log_service = 2;
  }
}

message VmConfig {
  ...
  map<string, LogDestination> log_destination

And the log ABI would be extended to accept a log destination string which would be mapped with that config.

[optional Relevant Links:]

https://github.com/envoyproxy/envoy/issues/22557#issuecomment-1205785100