Make transactions in execution layer integration tests (#3320)

## Issue Addressed

Resolves #3159 

## Proposed Changes

Sends transactions to the EE before requesting for a payload in the `execution_integration_tests`. Made some changes to the integration tests in order to be able to sign and publish transactions to the EE:

1. `genesis.json` for both geth and nethermind was modified to include pre-funded accounts that we know private keys for 
2. Using the unauthenticated port again in order to make `eth_sendTransaction` and calls from the `personal` namespace to import keys

Also added a `fcu` call with `PayloadAttributes` before calling `getPayload` in order to give EEs sufficient time to pack transactions into the payload.

testing/execution_engine_integration/src/execution_engine.rs

@@ -1,3 +1,4 @@
+use ethers_providers::{Http, Provider};
 use execution_layer::DEFAULT_JWT_FILE;
 use sensitive_url::SensitiveUrl;
 use std::path::PathBuf;
@@ -5,6 +6,14 @@ use std::process::Child;
 use tempfile::TempDir;
 use unused_port::unused_tcp_port;
 
+pub const KEYSTORE_PASSWORD: &str = "testpwd";
+pub const ACCOUNT1: &str = "7b8C3a386C0eea54693fFB0DA17373ffC9228139";
+pub const ACCOUNT2: &str = "dA2DD7560DB7e212B945fC72cEB54B7D8C886D77";
+pub const PRIVATE_KEYS: [&str; 2] = [
+    "115fe42a60e5ef45f5490e599add1f03c73aeaca129c2c41451eca6cf8ff9e04",
+    "6a692e710077d9000be1326acbe32f777b403902ac8779b19eb1398b849c99c3",
+];
+
 /// Defined for each EE type (e.g., Geth, Nethermind, etc).
 pub trait GenericExecutionEngine: Clone {
     fn init_datadir() -> TempDir;
@@ -22,8 +31,10 @@ pub struct ExecutionEngine<E> {
     engine: E,
     #[allow(dead_code)]
     datadir: TempDir,
+    http_port: u16,
     http_auth_port: u16,
     child: Child,
+    pub provider: Provider<Http>,
 }
 
 impl<E> Drop for ExecutionEngine<E> {
@@ -42,11 +53,15 @@ impl<E: GenericExecutionEngine> ExecutionEngine<E> {
         let http_port = unused_tcp_port().unwrap();
         let http_auth_port = unused_tcp_port().unwrap();
         let child = E::start_client(&datadir, http_port, http_auth_port, jwt_secret_path);
+        let provider = Provider::<Http>::try_from(format!("http://localhost:{}", http_port))
+            .expect("failed to instantiate ethers provider");
         Self {
             engine,
             datadir,
+            http_port,
             http_auth_port,
             child,
+            provider,
         }
     }
 
@@ -54,6 +69,10 @@ impl<E: GenericExecutionEngine> ExecutionEngine<E> {
         SensitiveUrl::parse(&format!("http://127.0.0.1:{}", self.http_auth_port)).unwrap()
     }
 
+    pub fn http_url(&self) -> SensitiveUrl {
+        SensitiveUrl::parse(&format!("http://127.0.0.1:{}", self.http_port)).unwrap()
+    }
+
     pub fn datadir(&self) -> PathBuf {
         self.datadir.path().to_path_buf()
     }