Add vc --disable-attesting flag

validator_client/src/cli.rs

@@ -97,6 +97,14 @@ pub struct ValidatorClient {
     )]
     pub disable_auto_discover: bool,
 
+    #[clap(
+        long,
+        help = "Disable everything except block proposals",
+        display_order = 0,
+        help_heading = FLAG_HEADER
+    )]
+    pub disable_attesting: bool,
+
     #[clap(
         long,
         help = "If present, the validator client will use longer timeouts for requests \