Only mark block lookups as pending if block is importing from gossip (#8112)

- PR https://github.com/sigp/lighthouse/pull/8045 introduced a regression of how lookup sync interacts with the da_checker.

Now in unstable block import from the HTTP API also insert the block in the da_checker while the block is being execution verified. If lookup sync finds the block in the da_checker in `NotValidated` state it expects a `GossipBlockProcessResult` message sometime later. That message is only sent after block import in gossip.

I confirmed in our node's logs for 4/4 cases of stuck lookups are caused by this sequence of events:
- Receive block through API, insert into da_checker in fn process_block in put_pre_execution_block
- Create lookup and leave in AwaitingDownload(block in processing cache) state
- Block from HTTP API finishes importing
- Lookup is left stuck

Closes https://github.com/sigp/lighthouse/issues/8104


  - https://github.com/sigp/lighthouse/pull/8110 was my initial solution attempt but we can't send the `GossipBlockProcessResult` event from the `http_api` crate without adding new channels, which seems messy.

For a given node it's rare that a lookup is created at the same time that a block is being published. This PR solves https://github.com/sigp/lighthouse/issues/8104 by allowing lookup sync to import the block twice in that case.


Co-Authored-By: dapplion <35266934+dapplion@users.noreply.github.com>

beacon_node/beacon_chain/src/beacon_chain.rs

@@ -334,7 +334,7 @@ pub enum BlockProcessStatus<E: EthSpec> {
     /// Block is not in any pre-import cache. Block may be in the data-base or in the fork-choice.
     Unknown,
     /// Block is currently processing but not yet validated.
-    NotValidated(Arc<SignedBeaconBlock<E>>),
+    NotValidated(Arc<SignedBeaconBlock<E>>, BlockImportSource),
     /// Block is fully valid, but not yet imported. It's cached in the da_checker while awaiting
     /// missing block components.
     ExecutionValidated(Arc<SignedBeaconBlock<E>>),
@@ -3351,8 +3351,11 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
             );
         }
 
-        self.data_availability_checker
-            .put_pre_execution_block(block_root, unverified_block.block_cloned())?;
+        self.data_availability_checker.put_pre_execution_block(
+            block_root,
+            unverified_block.block_cloned(),
+            block_source,
+        )?;
 
         // Start the Prometheus timer.
         let _full_timer = metrics::start_timer(&metrics::BLOCK_PROCESSING_TIMES);