feat: conditionally send aibridge actor headers (#21643)

Also passes along the authenticated username as actor metadata.

Closes https://github.com/coder/aibridge/issues/135
Depends on https://github.com/coder/aibridge/pull/142

**Replace aibridge tag with merge commit once
https://github.com/coder/aibridge/pull/142 lands.**

---------

Signed-off-by: Danny Kopping <danny@coder.com>

coderd/apidoc/docs.go

@@ -12075,6 +12075,9 @@ const docTemplate = `{
                 "retention": {
                     "type": "integer"
                 },
+                "send_actor_headers": {
+                    "type": "boolean"
+                },
                 "structured_logging": {
                     "type": "boolean"
                 }

coderd/apidoc/swagger.json

@@ -10727,6 +10727,9 @@
 				"retention": {
 					"type": "integer"
 				},
+				"send_actor_headers": {
+					"type": "boolean"
+				},
 				"structured_logging": {
 					"type": "boolean"
 				}