config: update minimum TLS version for server

The config is used both when setting up the HTTP API and
for the notifier's Deliverer.

Backports: #1945
Signed-off-by: Hank Donnay <[email protected]>
Signed-off-by: crozzy <[email protected]>
(cherry picked from commit 18aa1b3)

config/tls.go

@@ -55,6 +55,7 @@ func (t *TLS) Config() (*tls.Config, error) {
 		return nil, fmt.Errorf("failed to read x509 cert and key pair: %w", err)
 	}
 	cfg.Certificates = append(cfg.Certificates, cert)
+	cfg.MinVersion = tls.VersionTLS12
 
 	return &cfg, nil
 }