feat(cli): add enterprise external-workspaces CLI command (#19287)

This pull request introduces support for external workspace management, allowing users to register and manage workspaces that are provisioned and managed outside of the Coder.

* coder external-workspaces create - Creates a new external workspace (this command extends coder create)
  * Example: coder external-workspaces create ext-workspace --template=externally-managed-workspace -y
  * Checks if template has coder_external_agent resource before creating a workspace
* coder external-workspaces list - Lists all external workspaces
* coder external-workspaces agent-instructions <workspace name> <agent name> - Retrieves agent connection instruction
  * Example: coder external-workspaces agent-instructions ext-workspace main --output=json

docs/reference/cli/external-workspaces.md

@@ -0,0 +1,29 @@
+<!-- DO NOT EDIT | GENERATED CONTENT -->
+# external-workspaces
+
+Create or manage external workspaces
+
+## Usage
+
+```console
+coder external-workspaces [flags] [subcommand]
+```
+
+## Subcommands
+
+| Name                                                                           | Purpose                                    |
+|--------------------------------------------------------------------------------|--------------------------------------------|
+| [<code>create</code>](./external-workspaces_create.md)                         | Create a new external workspace            |
+| [<code>agent-instructions</code>](./external-workspaces_agent-instructions.md) | Get the instructions for an external agent |
+| [<code>list</code>](./external-workspaces_list.md)                             | List external workspaces                   |
+
+## Options
+
+### -O, --org
+
+|             |                                  |
+|-------------|----------------------------------|
+| Type        | <code>string</code>              |
+| Environment | <code>$CODER_ORGANIZATION</code> |
+
+Select which organization (uuid or name) to use.