feat: Adds filtering of erc20 tokens by their l2 address (#447)

# What ❔

Sometimes we only want a specific set of tokens or even no tokens at all
to be finalized. If we want no erc20 tokens to be finalized, say, in the
event that we only want to do ETH withdrawals, this option can be set to

```
ONLY_FINALIZE_THESE_TOKENS="[]"
```

## Why ❔

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## Checklist

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README.md

@@ -56,6 +56,7 @@ Deployment is done by deploying a dockerized image of the service.
 | `CUSTOM_TOKEN_ADDRESSES` | (Optional) Adds a predefined list of tokens to finalize. May be useful in case of custom bridge setups when the regular technique of finding token deployments does not work. |
 | `ENABLE_WITHDRAWAL_METERING` | (Optional, default: `"true"`) By default Finalizer collects metrics about withdrawn token volumens. Users may optionally switch off this metering. |
 | `ETH_FINALIZATION_THRESHOLD`| (Optional, default: "0") Finalizer will only finalize ETH withdrawals that are greater or equal to this value |
+| `ONLY_FINALIZE_THESE_TOKENS` | (Optional, default: `None`) If specified, creates a whitelist of erc20 tokens that will be finalized.
 
 The configuration structure describing the service config can be found in [`config.rs`](https://github.com/matter-labs/zksync-withdrawal-finalizer/blob/main/bin/withdrawal-finalizer/src/config.rs)
 

bin/withdrawal-finalizer/src/config.rs

@@ -86,6 +86,10 @@ pub struct Config {
 
     #[envconfig(from = "ONLY_L1_RECIPIENTS")]
     pub only_l1_recipients: Option<AddrList>,
+
+    /// Only finalize these tokens specified by their L2 addresses
+    #[envconfig(from = "ONLY_FINALIZE_THESE_TOKENS")]
+    pub only_finalize_these_tokens: Option<AddrList>,
 }
 
 #[derive(Deserialize, Serialize, Debug, Eq, PartialEq)]

bin/withdrawal-finalizer/src/main.rs

@@ -202,11 +202,16 @@ async fn main() -> Result<()> {
         tokens.extend_from_slice(custom_tokens.0.as_slice());
     }
 
-    tracing::info!("tokens {tokens:?}");
     if let Some(ref custom_tokens) = config.custom_token_deployer_addresses {
         tokens.extend_from_slice(custom_tokens.0.as_slice());
     }
 
+    if let Some(only_finalize_these_tokens) = config.only_finalize_these_tokens {
+        tokens.retain(|token| only_finalize_these_tokens.0.contains(token));
+    }
+
+    tracing::info!("tokens {tokens:?}");
+
     let l2_events = L2EventsListener::new(
         config.api_web3_json_rpc_ws_url.as_str(),
         config