http conn man: add tracing config for path length in tag (#8095)

This PR adds a configuration option for controlling the length of the request path that is included in the HttpUrl span tag. Currently, this length is hard-coded to 256. With this PR, that length will be configurable (defaulting to the old value).

Risk Level: Low
Testing: Unit
Docs Changes: Inline with the API proto. Documented new field.
Release Notes: Added in the PR.

Related issue: istio/istio#14563

Signed-off-by: Douglas Reid <douglas-reid@users.noreply.github.com>

Mirrored from https://github.com/envoyproxy/envoy @ 277e7175091cdf9d6c8732bc40381ff4e0fee48c

envoy/config/filter/network/http_connection_manager/v2/http_connection_manager.proto

@@ -130,6 +130,11 @@ message HttpConnectionManager {
     // Whether to annotate spans with additional data. If true, spans will include logs for stream
     // events.
     bool verbose = 6;
+
+    // Maximum length of the request path to extract and include in the HttpUrl tag. Used to
+    // truncate lengthy request paths to meet the needs of a tracing backend.
+    // Default: 256
+    google.protobuf.UInt32Value max_path_tag_length = 7;
   }
 
   // Presence of the object defines whether the connection manager