feat: add OpenIn option to coder_app (#15743)

This PR is the coder/coder part of [the open_in parameter
issue](https://github.com/coder/terraform-provider-coder/issues/297)
aiming to add a new optional parameter to choose how to open modules.

This PR is heavily linked [to this
PR](https://github.com/coder/terraform-provider-coder/pull/321).

ℹ️ For now, some integrations tests can not be pushed as it requires a
release on the terraform-provider repo.

coderd/apidoc/docs.go

@@ -15079,6 +15079,9 @@ const docTemplate = `{
                     "type": "string",
                     "format": "uuid"
                 },
+                "open_in": {
+                    "type": "string"
+                },
                 "sharing_level": {
                     "enum": [
                         "owner",

coderd/apidoc/swagger.json

@@ -13728,6 +13728,9 @@
 					"type": "string",
 					"format": "uuid"
 				},
+				"open_in": {
+					"type": "string"
+				},
 				"sharing_level": {
 					"enum": ["owner", "authenticated", "public"],
 					"allOf": [