detect/http2: warning that http2.header is removed

in Suricata 7

Ticket: #5780

src/detect-http2.c

@@ -806,6 +806,10 @@ static int DetectEngineInspectHttp2HeaderName(
 
 static int DetectHTTP2headerSetup(DetectEngineCtx *de_ctx, Signature *s, const char *arg)
 {
+    SCLogWarning(SC_WARN_DEPRECATED,
+            "Experimental keyword http2.header is removed in Suricata 7, and replaced "
+            "by http.request_header and http.response_header, see "
+            "https://redmine.openinfosecfoundation.org/issues/5780");
     if (DetectBufferSetActiveList(s, g_http2_header_buffer_id) < 0)
         return -1;