Validator manager commands for the Keymanager APIs

[chong-he]

Issue Addressed

• Validator manager commands for standard key-manager APIs #4854

Proposed Changes

Add commonds to lighthouse vm to support the Keymanager API to manage local keystores, i.e., list, import and delete

Additional Info

Building on top of @pahor167 PR: #5347

[eserilev]

If it's not too much of a hassle it'd be cool to define the new cli flags here w/ clap derive. Alternatively, I can make a separate PR to migrate to derive once this is merged

EDIT: I think we can just migrate to clap derive later after this PR is merged. thanks for taking a look CK!

[macladson]

This looks very clean!
I do have a few suggestions for you which range from easy fixes to large rewrites 😁

[macladson]

There's a decent amount of code duplication between this and the import_validators.rs file.

It would be nice if would could merge the two into the same command, with maybe a --use-standard-format flag or something in order to specify which format we are using (next level would be detecting which format it is automagically. I believe we can also make certain flags mutually exclusive so we can disable the ones that are not applicable for each format.

This may not be worth the complexity, but it's just quite unintuitive (imo) to have an import subcommand and then also an import-standard subcommand.