Update is_available check to support PeerDAS. (#6076)

* Update `is_available` check to support PeerDAS.

* Merge branch 'unstable' into da-checker-das

# Conflicts:
#	beacon_node/beacon_chain/src/data_availability_checker.rs
#	beacon_node/beacon_chain/src/data_availability_checker/overflow_lru_cache.rs

* Simplify code using `map_or`

* Merge branch 'unstable' into da-checker-das

# Conflicts:
#	consensus/types/src/chain_spec.rs

* Remove `epoch` method from `PendingComponents`

* Add `put_kzg_verified_data_columns` method.

beacon_node/beacon_chain/src/data_column_verification.rs

@@ -0,0 +1,19 @@
+use derivative::Derivative;
+use ssz_derive::{Decode, Encode};
+use std::sync::Arc;
+use types::data_column_sidecar::{ColumnIndex, DataColumnSidecar};
+use types::EthSpec;
+
+/// Data column that we must custody and has completed kzg verification
+#[derive(Debug, Derivative, Clone, Encode, Decode)]
+#[derivative(PartialEq, Eq)]
+#[ssz(struct_behaviour = "transparent")]
+pub struct KzgVerifiedCustodyDataColumn<E: EthSpec> {
+    data: Arc<DataColumnSidecar<E>>,
+}
+
+impl<E: EthSpec> KzgVerifiedCustodyDataColumn<E> {
+    pub fn index(&self) -> ColumnIndex {
+        self.data.index
+    }
+}