command line tools for redacting keyring from snapshots (#24023)

In #23977 we moved the keyring into Raft, which can expose key material in Raft
snapshots when using the less-secure AEAD keyring instead of KMS. This changeset
adds tools for redacting this material from snapshots:

* The `operator snapshot state` command gains the ability to display key
  metadata (only), which respects the `-filter` option.
* The `operator snapshot save` command gains a `-redact` option that removes key
  material from the snapshot after it's downloaded.
* A new `operator snapshot redact` command allows removing key material from an
  existing snapshot.

website/data/docs-nav-data.json

@@ -937,6 +937,10 @@
                 "title": "inspect",
                 "path": "commands/operator/snapshot/inspect"
               },
+              {
+                "title": "redact",
+                "path": "commands/operator/snapshot/redact"
+              },
               {
                 "title": "restore",
                 "path": "commands/operator/snapshot/restore"