Storing sensitive information in a SQL Server project
You've got to put these things somewhere, where they are:


accessible only to the people who should have access to them;
protected from the people who shouldn't; and,
recoverable in the event of any disaster (be it people moving on or machines getting thrown in a tar pit). 


But only you can know where that somewhere is in your environment. It could very well be source control (but probably not); Azure Key Vault is an option, depending on how cloud-averse your business is; some companies use a service like Enterprise LastPass or 1Password Business; or maybe a sticky note on Milton's red stapler is more your speed... as your peers and not business stakeholders, we just don't know.