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/database/dump.sql

@@ -261,6 +261,12 @@ CREATE TYPE workspace_app_health AS ENUM (
     'unhealthy'
 );
 
+CREATE TYPE workspace_app_open_in AS ENUM (
+    'tab',
+    'window',
+    'slim-window'
+);
+
 CREATE TYPE workspace_transition AS ENUM (
     'start',
     'stop',
@@ -1602,7 +1608,8 @@ CREATE TABLE workspace_apps (
     slug text NOT NULL,
     external boolean DEFAULT false NOT NULL,
     display_order integer DEFAULT 0 NOT NULL,
-    hidden boolean DEFAULT false NOT NULL
+    hidden boolean DEFAULT false NOT NULL,
+    open_in workspace_app_open_in DEFAULT 'slim-window'::workspace_app_open_in NOT NULL
 );
 
 COMMENT ON COLUMN workspace_apps.display_order IS 'Specifies the order in which to display agent app in user interfaces.';