Modularize validator store (#6705)

- Create trait `ValidatorStore` with all functions used by the `validator_services`
- Make `validator_services` generic on `S: ValidatorStore`
- Introduce `LighthouseValidatorStore`, which has identical functionality to the old `ValidatorStore`
- Remove dependencies (especially `environment`) from `validator_services` and `beacon_node_fallback` in order to be able to cleanly use them in Anchor

validator_client/http_api/src/tests/keystores.rs

@@ -8,12 +8,13 @@ use eth2::lighthouse_vc::{
     types::Web3SignerValidatorRequest,
 };
 use itertools::Itertools;
+use lighthouse_validator_store::DEFAULT_GAS_LIMIT;
 use rand::{rngs::SmallRng, Rng, SeedableRng};
 use slashing_protection::interchange::{Interchange, InterchangeMetadata};
 use std::{collections::HashMap, path::Path};
 use tokio::runtime::Handle;
 use types::{attestation::AttestationBase, Address};
-use validator_store::DEFAULT_GAS_LIMIT;
+use validator_store::ValidatorStore;
 use zeroize::Zeroizing;
 
 fn new_keystore(password: Zeroizing<String>) -> Keystore {