extension mechanism for custom logs and span attributes (#1451)

plugins/wasm-go/examples/custom-log/config.yaml

@@ -0,0 +1,68 @@
+static_resources:
+  listeners:
+  - name: listener_0
+    address:
+      socket_address:
+        protocol: TCP
+        address: 0.0.0.0
+        port_value: 8080
+    filter_chains:
+    - filters:
+      - name: envoy.filters.network.http_connection_manager
+        typed_config:
+          "@type": type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager
+          stat_prefix: ingress_http
+          access_log:
+          - name: envoy.access_loggers.file
+            typed_config:
+              "@type": type.googleapis.com/envoy.extensions.access_loggers.file.v3.FileAccessLog
+              log_format:
+                text_format_source:
+                  inline_string: "{\"custom_log\":\"%FILTER_STATE(wasm.custom_log:PLAIN)%\",\"ai_log\":\"%FILTER_STATE(wasm.ai_log:PLAIN)%\"}
+                  
+                  "
+              path: /dev/stdout
+          route_config:
+            name: local_route
+            virtual_hosts:
+            - name: local_service
+              domains: ["*"]
+              routes:
+              - name: get
+                match:
+                  prefix: "/get"
+                route:
+                  cluster: httpbin
+          http_filters:
+          - name: test
+            typed_config:
+              "@type": type.googleapis.com/udpa.type.v1.TypedStruct
+              type_url: type.googleapis.com/envoy.extensions.filters.http.wasm.v3.Wasm
+              value:
+                config:
+                  name: test
+                  vm_config:
+                    runtime: envoy.wasm.runtime.v8
+                    code:
+                      local:
+                        filename: main.wasm
+                  configuration:
+                    "@type": "type.googleapis.com/google.protobuf.StringValue"
+                    value: {}
+          - name: envoy.filters.http.router
+            typed_config:
+              "@type": type.googleapis.com/envoy.extensions.filters.http.router.v3.Router
+  clusters:
+  - name: httpbin
+    connect_timeout: 600s
+    type: STRICT_DNS
+    lb_policy: ROUND_ROBIN
+    load_assignment:
+      cluster_name: httpbin
+      endpoints:
+        - lb_endpoints:
+          - endpoint:
+              address:
+                socket_address:
+                  address: httpbin.org
+                  port_value: 80