Encode Execution Engine Client Version In Graffiti (#5290)

* Add `engine_clientVersionV1` structs

* Implement `engine_clientVersionV1`

* Update to latest spec changes

* Implement GraffitiCalculator Service

* Added Unit Tests for GraffitiCalculator

* Address Mac's Comments

* Remove need to use clap in beacon chain

* Merge remote-tracking branch 'upstream/unstable' into el_client_version_graffiti

* Merge branch 'unstable' into el_client_version_graffiti

# Conflicts:
#	beacon_node/beacon_chain/Cargo.toml

consensus/types/src/graffiti.rs

@@ -47,6 +47,12 @@ impl Into<[u8; GRAFFITI_BYTES_LEN]> for Graffiti {
 #[serde(transparent)]
 pub struct GraffitiString(String);
 
+impl GraffitiString {
+    pub fn empty() -> Self {
+        Self(String::new())
+    }
+}
+
 impl FromStr for GraffitiString {
     type Err = String;