Add EF launchpad import (#1381)

## Issue Addressed

NA

## Proposed Changes

Adds an integration for keys generated via https://github.com/ethereum/eth2.0-deposit (In reality keys are *actually* generated here: https://github.com/ethereum/eth2.0-deposit-cli).

## Additional Info

NA

## TODO

- [x] Docs
- [x] Tests

Co-authored-by: Michael Sproul <michael@sigmaprime.io>

validator_client/src/config.rs

@@ -80,13 +80,6 @@ impl Config {
             config.secrets_dir = secrets_dir;
         }
 
-        if !config.secrets_dir.exists() {
-            return Err(format!(
-                "The directory for validator passwords (--secrets-dir) does not exist: {:?}",
-                config.secrets_dir
-            ));
-        }
-
         Ok(config)
     }
 }