Add ability to autogenerate md5 keys in net-vpn-ha (#2748)

* Add ability to optionally generate MD5 secrets in VPN module

* Add ability to autogenerate MD5 keys in net-vpn-ha module

* restore missing output

* fix test counts

---------

Co-authored-by: Luca Prete <lucaprete@google.com>
Co-authored-by: Ludovico Magnocavallo <ludomagno@google.com>

blueprints/apigee/network-patterns/nb-glb-psc-neg-sb-psc-ilbl7-hybrid-neg/README.md

@@ -79,5 +79,5 @@ module "test" {
   onprem_project_id  = "my-onprem-project"
   hostname           = "test.myorg.org"
 }
-# tftest modules=14 resources=80
+# tftest modules=14 resources=84
 ```

blueprints/networking/private-cloud-function-from-onprem/README.md

@@ -45,5 +45,5 @@ module "test" {
   }
   project_id = "test-project"
 }
-# tftest modules=11 resources=50
+# tftest modules=11 resources=54
 ```

blueprints/networking/vpc-connectivity-lab/README.md

@@ -108,5 +108,5 @@ module "test" {
   prefix     = "fast-sr0-sbox"
 }
 
-# tftest modules=35 resources=136
+# tftest modules=35 resources=144
 ```

blueprints/serverless/cloud-run-corporate/README.md

@@ -253,7 +253,7 @@ module "test" {
   prj_onprem_id = "onprem-project-id"
 }
 
-# tftest modules=15 resources=58
+# tftest modules=15 resources=62
 ```
 
 ```hcl