Support of unverified smtp server

[sm-ghavami]

Expectation / Proposal

Self-signed certificates are often used in private or isolated network environments where obtaining a trusted certificate authority-signed certificate is not feasible or necessary. As a result, Prefect Email users who operate in such environments are unable to use the Email feature due to the current lack of support for self-signed SMTP servers. We should add an attribute to credentials which indicates the server is self-signed or not.