Don't init datadir if it doesn't exist in db command

[mattsse]

Describe the feature

this will always initialize the dir:

reth/crates/cli/commands/src/db/mod.rs

Line 56 in 405b730

let Environment { provider_factory, .. } = $env.init(AccessRights::RO)?;

this shouldn't be the case if --datadir does not exist

TODO

• ensure provided datadir exists in db command

Additional context

running db against a non existing datadir will create it:

reth db --datadir ../does-not-exist clear mdbx StoragesTrie

[yutianwu]

can I take this?

[mattsse]

assigned, ty