feat: add CLI support for user secrets (#24270)

Adds a coder secret command group for managing user secrets from the
CLI, with create, update, list, and delete subcommands backed by the
existing user secret API.

This branch adds CLI test coverage and refreshes the generated help
output and CLI reference docs for the new command group.

docs/reference/cli/secret.md

@@ -0,0 +1,47 @@
+<!-- DO NOT EDIT | GENERATED CONTENT -->
+# secret
+
+Manage secrets
+
+Aliases:
+
+* secrets
+
+## Usage
+
+```console
+coder secret
+```
+
+## Description
+
+```console
+  - Create a secret:
+
+     $ printf %s "$MYCLI_API_KEY" | coder secret create api-key --description "API key for workspace tools" --env API_KEY --file "~/.api-key"
+
+  - Update a secret:
+
+     $ echo -n "$NEW_SECRET_VALUE" | coder secret update api-key --description "Rotated API key" --env API_KEY --file "~/.api-key"
+
+  - List your secrets:
+
+     $ coder secret list
+
+  - Show a specific secret:
+
+     $ coder secret list api-key
+
+  - Delete a secret:
+
+     $ coder secret delete api-key
+```
+
+## Subcommands
+
+| Name                                      | Purpose                           |
+|-------------------------------------------|-----------------------------------|
+| [<code>create</code>](./secret_create.md) | Create a secret                   |
+| [<code>update</code>](./secret_update.md) | Update a secret                   |
+| [<code>list</code>](./secret_list.md)     | List secrets, or show one by name |
+| [<code>delete</code>](./secret_delete.md) | Delete a secret                   |