Disallow genesis sync outside blob pruning window (#5038)

* Disallow Syncing From Genesis By Default

* Fix CLI Tests

* Perform checks in the `ClientBuilder`

* Tidy, fix tests

* Return an error based on the Deneb fork

* Fix typos

* Fix failing test

* Add missing CLI flag

* Fix CLI flags

* Add suggestion from Sean

* Fix conflict with blob sidecars epochs

---------

Co-authored-by: Mark Mackey <mark@sigmaprime.io>

beacon_node/src/cli.rs

@@ -955,6 +955,16 @@ pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
                 .takes_value(true)
                 .default_value("180")
         )
+        .arg(
+            Arg::with_name("allow-insecure-genesis-sync")
+                .long("allow-insecure-genesis-sync")
+                .help("Enable syncing from genesis, which is generally insecure and incompatible with data availability checks. \
+                    Checkpoint syncing is the preferred method for syncing a node. \
+                    Only use this flag when testing. DO NOT use on mainnet!")
+                .conflicts_with("checkpoint-sync-url")
+                .conflicts_with("checkpoint-state")
+                .takes_value(false)
+        )
         .arg(
             Arg::with_name("reconstruct-historic-states")
                 .long("reconstruct-historic-states")