Avoid Printing Binary String to Logs (#1576)

Converts the graffiti binary data to string before printing to logs.

## Issue Addressed

#1566 

## Proposed Changes
Rather than converting graffiti to a vector the binary data less the last character is passed to String::from_utf_lossy(). This then allows us to call the to_string() function directly to give us the string

## Additional Info

Rust skills are fairly weak

beacon_node/beacon_chain/Cargo.toml

@@ -58,3 +58,4 @@ environment = { path = "../../lighthouse/environment" }
 bus = "2.2.3"
 derivative = "2.1.1"
 itertools = "0.9.0"
+regex = "1.3.9"