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/lighthouse_network/src/peer_manager/peerdb/client.rs

@@ -4,7 +4,7 @@
 
 use libp2p::identify::IdentifyInfo;
 use serde::Serialize;
-use strum::{AsRefStr, AsStaticStr, EnumIter};
+use strum::{AsRefStr, EnumIter, IntoStaticStr};
 
 /// Various client and protocol information related to a node.
 #[derive(Clone, Debug, Serialize)]
@@ -21,7 +21,7 @@ pub struct Client {
     pub agent_string: Option<String>,
 }
 
-#[derive(Clone, Debug, Serialize, PartialEq, AsRefStr, AsStaticStr, EnumIter)]
+#[derive(Clone, Copy, Debug, Serialize, PartialEq, AsRefStr, IntoStaticStr, EnumIter)]
 pub enum ClientKind {
     /// A lighthouse node (the best kind).
     Lighthouse,