Add introducer add command

- Create a command to add an introducer (with domains).
- Add a module for escaping regular expressions used in certifications
- Add some helper functions.

Cargo.toml

@@ -11,6 +11,7 @@ categories = ["cryptography", "email"]
 rust-version = "1.85"
 
 [dependencies]
+aho-corasick = "1.1.4"
 anyhow = "1.0.100"
 bytes = "1.11.1"
 clap = { version = "4", features = ["derive"] }