feat(cli): add open app <workspace> <app-slug> command (#17032)

Fixes https://github.com/coder/coder/issues/17009

Adds a CLI command `coder open app <workspace> <app-slug>` that allows
opening arbitrary `coder_apps` via the CLI.

Users can optionally specify a region for workspace
applications.

docs/reference/cli/open.md

@@ -14,3 +14,4 @@ coder open
 | Name                                    | Purpose                             |
 |-----------------------------------------|-------------------------------------|
 | [<code>vscode</code>](./open_vscode.md) | Open a workspace in VS Code Desktop |
+| [<code>app</code>](./open_app.md)       | Open a workspace application.       |

docs/reference/cli/open_app.md

@@ -0,0 +1,22 @@
+<!-- DO NOT EDIT | GENERATED CONTENT -->
+# open app
+
+Open a workspace application.
+
+## Usage
+
+```console
+coder open app [flags] <workspace> <app slug>
+```
+
+## Options
+
+### --region
+
+|             |                                     |
+|-------------|-------------------------------------|
+| Type        | <code>string</code>                 |
+| Environment | <code>$CODER_OPEN_APP_REGION</code> |
+| Default     | <code>primary</code>                |
+
+Region to use when opening the app. By default, the app will be opened using the main Coder deployment (a.k.a. "primary").