Pseudo finalization endpoint (#7103)

This is a backport of:
-  https://github.com/sigp/lighthouse/pull/7059
- https://github.com/sigp/lighthouse/pull/7071

For:
- https://github.com/sigp/lighthouse/issues/7039


  Introduce a new lighthouse endpoint that allows a user to force a pseudo finalization. This migrates data to the freezer db and prunes sidechains which may help reduce disk space issues on non finalized networks like Holesky

We also ban peers that send us blocks that conflict with the manually finalized checkpoint.

There were some CI fixes in https://github.com/sigp/lighthouse/pull/7071 that I tried including here

Co-authored with: @jimmygchen  @pawanjay176 @michaelsproul

beacon_node/beacon_chain/src/block_verification.rs

@@ -1767,7 +1767,22 @@ pub fn check_block_is_finalized_checkpoint_or_descendant<
     fork_choice: &BeaconForkChoice<T>,
     block: B,
 ) -> Result<B, BlockError> {
-    if fork_choice.is_finalized_checkpoint_or_descendant(block.parent_root()) {
+    // If we have a split block newer than finalization then we also ban blocks which are not
+    // descended from that split block. It's important not to try checking `is_descendant` if
+    // finality is ahead of the split and the split block has been pruned, as `is_descendant` will
+    // return `false` in this case.
+    let finalized_slot = fork_choice
+        .finalized_checkpoint()
+        .epoch
+        .start_slot(T::EthSpec::slots_per_epoch());
+    let split = chain.store.get_split_info();
+    let is_descendant_from_split_block = split.slot == 0
+        || split.slot <= finalized_slot
+        || fork_choice.is_descendant(split.block_root, block.parent_root());
+
+    if fork_choice.is_finalized_checkpoint_or_descendant(block.parent_root())
+        && is_descendant_from_split_block
+    {
         Ok(block)
     } else {
         // If fork choice does *not* consider the parent to be a descendant of the finalized block,