Secure gRPC TLS: remove InsecureSkipVerify and enable proper CA verification

[viktorking7]

Description

• Removed insecure InsecureSkipVerify: true and set RootCAs to the provided CA pool to restore server certificate verification.
• Kept mTLS settings intact (ClientCAs, ClientAuth: RequireAndVerifyClientCert) and enforced MinVersion: TLS1.2.
• Improves security against MitM by validating the server’s cert chain.

Impact

• More secure client connections; no interface changes required.
• If hostname verification is desired, consider a follow-up to set tls.Config.ServerName via a dedicated ClientTLS(...).