feat(vpn): Add Site-to-Site VPN management initially for AWS and Azure (#164)

- Created templates for AWS and Azure VPN resources, which consist of each CSP's VPN gateway resource and VPN connection module between the two.
- Enhanced variable definitions for VPN configuration in the infracode, ensuring flexibility and clarity in resource management.
- Added REST API handlers for Site-to-Site VPN operations, including Create, Get, and Delete.
- Implemented validation logic for VPN configuration, ensuring correct parameters are provided.
- Added `apipa_cidrs` property for Azure configuration and updated infracode.
- Updated API docs.
- Tested for functionality and API operation.

Author: yunkon-kim

api/docs.go

@@ -432,7 +432,7 @@ func outputAwsToSiteVpn(c echo.Context) (model.Response, error) {
 	case DetailOptions.Refined:
 
 		/*
-		 * NOTE: Set the output object (e.g., "testbed_info") to get the refined resource info
+		 * NOTE: Set the output object (e.g., "vpn_info") to get the refined resource info
 		 */
 
 		trInfo, exists, err := terrarium.GetInfo(trId)