feat(site): connect open_in parameter (#16036)

Second step to resolve [open_in
issue](https://github.com/coder/terraform-provider-coder/issues/297)

This PR improves the way the open_in parameter is forwarded across the
code, changing the last `string` to const everywhere.

Also make sure it is available and forwarded up to the `CreateLink`
component.

coderd/apidoc/docs.go

@@ -15080,7 +15080,7 @@ const docTemplate = `{
                     "format": "uuid"
                 },
                 "open_in": {
-                    "type": "string"
+                    "$ref": "#/definitions/codersdk.WorkspaceAppOpenIn"
                 },
                 "sharing_level": {
                     "enum": [
@@ -15127,6 +15127,19 @@ const docTemplate = `{
                 "WorkspaceAppHealthUnhealthy"
             ]
         },
+        "codersdk.WorkspaceAppOpenIn": {
+            "type": "string",
+            "enum": [
+                "slim-window",
+                "window",
+                "tab"
+            ],
+            "x-enum-varnames": [
+                "WorkspaceAppOpenInSlimWindow",
+                "WorkspaceAppOpenInWindow",
+                "WorkspaceAppOpenInTab"
+            ]
+        },
         "codersdk.WorkspaceAppSharingLevel": {
             "type": "string",
             "enum": [