Add default values to aws_vpn_connection (#17031)

* Add default values to aws_vpn_connection

This fixes a bug where removing fields from the resource should revert
them to their default value, but instead sets them to their empty value
(in this case 0). When this happens the provider attempts to use these 0
values to update the VPN connection which results in an error, forcing
the user to specify these fields and their default values.

Signed-off-by: Stephen Hoekstra <shoekstra@schubergphilis.com>

.changelog/17031.txt

@@ -0,0 +1,3 @@
+```release-note:enhancement
+resource/aws_vpn_connection: Add the ability to revert changes to unconfigured tunnel options made outside of Terraform to their (documented default values)[(https://docs.aws.amazon.com/vpn/latest/s2svpn/VPNTunnels.html)]
+```

internal/service/ec2/enum.go

@@ -58,6 +58,108 @@ const (
 	CustomerGatewayStatePending   = "pending"
 )
 
+const (
+	VpnTunnelOptionsDPDTimeoutActionClear   = "clear"
+	VpnTunnelOptionsDPDTimeoutActionNone    = "none"
+	VpnTunnelOptionsDPDTimeoutActionRestart = "restart"
+)
+
+func VpnTunnelOptionsDPDTimeoutAction_Values() []string {
+	return []string{
+		VpnTunnelOptionsDPDTimeoutActionClear,
+		VpnTunnelOptionsDPDTimeoutActionNone,
+		VpnTunnelOptionsDPDTimeoutActionRestart,
+	}
+}
+
+const (
+	VpnTunnelOptionsIKEVersion1 = "ikev1"
+	VpnTunnelOptionsIKEVersion2 = "ikev2"
+)
+
+func VpnTunnelOptionsIKEVersion_Values() []string {
+	return []string{
+		VpnTunnelOptionsIKEVersion1,
+		VpnTunnelOptionsIKEVersion2,
+	}
+}
+
+const (
+	VpnTunnelOptionsPhase1EncryptionAlgorithmAES128        = "AES128"
+	VpnTunnelOptionsPhase1EncryptionAlgorithmAES256        = "AES256"
+	VpnTunnelOptionsPhase1EncryptionAlgorithmAES128_GCM_16 = "AES128-GCM-16"
+	VpnTunnelOptionsPhase1EncryptionAlgorithmAES256_GCM_16 = "AES256-GCM-16"
+)
+
+func VpnTunnelOptionsPhase1EncryptionAlgorithm_Values() []string {
+	return []string{
+		VpnTunnelOptionsPhase1EncryptionAlgorithmAES128,
+		VpnTunnelOptionsPhase1EncryptionAlgorithmAES256,
+		VpnTunnelOptionsPhase1EncryptionAlgorithmAES128_GCM_16,
+		VpnTunnelOptionsPhase1EncryptionAlgorithmAES256_GCM_16,
+	}
+}
+
+const (
+	VpnTunnelOptionsPhase1IntegrityAlgorithmSHA1     = "SHA1"
+	VpnTunnelOptionsPhase1IntegrityAlgorithmSHA2_256 = "SHA2-256"
+	VpnTunnelOptionsPhase1IntegrityAlgorithmSHA2_384 = "SHA2-384"
+	VpnTunnelOptionsPhase1IntegrityAlgorithmSHA2_512 = "SHA2-512"
+)
+
+func VpnTunnelOptionsPhase1IntegrityAlgorithm_Values() []string {
+	return []string{
+		VpnTunnelOptionsPhase1IntegrityAlgorithmSHA1,
+		VpnTunnelOptionsPhase1IntegrityAlgorithmSHA2_256,
+		VpnTunnelOptionsPhase1IntegrityAlgorithmSHA2_384,
+		VpnTunnelOptionsPhase1IntegrityAlgorithmSHA2_512,
+	}
+}
+
+const (
+	VpnTunnelOptionsPhase2EncryptionAlgorithmAES128        = "AES128"
+	VpnTunnelOptionsPhase2EncryptionAlgorithmAES256        = "AES256"
+	VpnTunnelOptionsPhase2EncryptionAlgorithmAES128_GCM_16 = "AES128-GCM-16"
+	VpnTunnelOptionsPhase2EncryptionAlgorithmAES256_GCM_16 = "AES256-GCM-16"
+)
+
+func VpnTunnelOptionsPhase2EncryptionAlgorithm_Values() []string {
+	return []string{
+		VpnTunnelOptionsPhase2EncryptionAlgorithmAES128,
+		VpnTunnelOptionsPhase2EncryptionAlgorithmAES256,
+		VpnTunnelOptionsPhase2EncryptionAlgorithmAES128_GCM_16,
+		VpnTunnelOptionsPhase2EncryptionAlgorithmAES256_GCM_16,
+	}
+}
+
+const (
+	VpnTunnelOptionsPhase2IntegrityAlgorithmSHA1     = "SHA1"
+	VpnTunnelOptionsPhase2IntegrityAlgorithmSHA2_256 = "SHA2-256"
+	VpnTunnelOptionsPhase2IntegrityAlgorithmSHA2_384 = "SHA2-384"
+	VpnTunnelOptionsPhase2IntegrityAlgorithmSHA2_512 = "SHA2-512"
+)
+
+func VpnTunnelOptionsPhase2IntegrityAlgorithm_Values() []string {
+	return []string{
+		VpnTunnelOptionsPhase2IntegrityAlgorithmSHA1,
+		VpnTunnelOptionsPhase2IntegrityAlgorithmSHA2_256,
+		VpnTunnelOptionsPhase2IntegrityAlgorithmSHA2_384,
+		VpnTunnelOptionsPhase2IntegrityAlgorithmSHA2_512,
+	}
+}
+
+const (
+	VpnTunnelOptionsStartupActionAdd   = "add"
+	VpnTunnelOptionsStartupActionStart = "start"
+)
+
+func VpnTunnelOptionsStartupAction_Values() []string {
+	return []string{
+		VpnTunnelOptionsStartupActionAdd,
+		VpnTunnelOptionsStartupActionStart,
+	}
+}
+
 const (
 	VpnConnectionTypeIpsec1 = "ipsec.1"
 )