feat: Make executors_file_path optional and use a default value if None

--- don't change below this line ---
ENG-4088 Took 4 minutes

Took 59 seconds

src/encoding/evm/constants.rs

@@ -0,0 +1 @@
+pub const DEFAULT_EXECUTORS_FILE_PATH: &str = "src/encoding/config/executor_addresses.json";