chore(validation): move functions from constants

- Move validation functions from `internal/constants` to `internal/configuration/settings/validation`
- Concatenate all OpenVPN constants in `internal/constants/openvpn.go`

internal/provider/surfshark/openvpnconf.go

@@ -73,9 +73,9 @@ func (s *Surfshark) BuildConf(connection models.Connection,
 	}
 
 	lines = append(lines, utils.WrapOpenvpnCA(
-		constants.SurfsharkCertificate)...)
+		constants.SurfsharkCA)...)
 	lines = append(lines, utils.WrapOpenvpnTLSAuth(
-		constants.SurfsharkOpenvpnStaticKeyV1)...)
+		constants.SurfsharkTLSAuth)...)
 
 	lines = append(lines, "")