Add lighthouse db command (#3129)

## Proposed Changes

Add a `lighthouse db` command with three initial subcommands:

- `lighthouse db version`: print the database schema version.
- `lighthouse db migrate --to N`: manually upgrade (or downgrade!) the database to a different version.
- `lighthouse db inspect --column C`: log the key and size in bytes of every value in a given `DBColumn`.

This PR lays the groundwork for other changes, namely:

- Mark's fast-deposit sync (https://github.com/sigp/lighthouse/pull/2915), for which I think we should implement a database downgrade (from v9 to v8).
- My `tree-states` work, which already implements a downgrade (v10 to v8).
- Standalone purge commands like `lighthouse db purge-dht` per https://github.com/sigp/lighthouse/issues/2824.

## Additional Info

I updated the `strum` crate to 0.24.0, which necessitated some changes in the network code to remove calls to deprecated methods.

Thanks to @winksaville for the motivation, and implementation work that I used as a source of inspiration (https://github.com/sigp/lighthouse/pull/2685).

beacon_node/network/src/metrics.rs

@@ -9,7 +9,6 @@ use lighthouse_network::{
     Gossipsub, NetworkGlobals,
 };
 use std::sync::Arc;
-use strum::AsStaticRef;
 use strum::IntoEnumIterator;
 use types::EthSpec;
 
@@ -357,12 +356,12 @@ pub fn update_gossip_metrics<T: EthSpec>(
     for client_kind in ClientKind::iter() {
         set_gauge_vec(
             &BEACON_BLOCK_MESH_PEERS_PER_CLIENT,
-            &[&client_kind.to_string()],
+            &[client_kind.as_ref()],
             0_i64,
         );
         set_gauge_vec(
             &BEACON_AGGREGATE_AND_PROOF_MESH_PEERS_PER_CLIENT,
-            &[&client_kind.to_string()],
+            &[client_kind.as_ref()],
             0_i64,
         );
     }
@@ -377,7 +376,7 @@ pub fn update_gossip_metrics<T: EthSpec>(
                             .peers
                             .read()
                             .peer_info(peer_id)
-                            .map(|peer_info| peer_info.client().kind.as_static())
+                            .map(|peer_info| peer_info.client().kind.into())
                             .unwrap_or_else(|| "Unknown");
                         if let Some(v) =
                             get_int_gauge(&BEACON_BLOCK_MESH_PEERS_PER_CLIENT, &[client])
@@ -392,7 +391,7 @@ pub fn update_gossip_metrics<T: EthSpec>(
                             .peers
                             .read()
                             .peer_info(peer_id)
-                            .map(|peer_info| peer_info.client().kind.as_static())
+                            .map(|peer_info| peer_info.client().kind.into())
                             .unwrap_or_else(|| "Unknown");
                         if let Some(v) = get_int_gauge(
                             &BEACON_AGGREGATE_AND_PROOF_MESH_PEERS_PER_CLIENT,