docs: add deprecation warning for login-type none (#24594)

The `--login-type none` option for `coder users create` is deprecated.
This adds deprecation warnings to all docs that reference it and updates
the CI/CD tutorial to recommend the replacement flows.

Refs DEVEX-224

<details>
<summary>Changes</summary>

- `cli/usercreate.go`: Append deprecation notice to `--login-type` flag
description.
- `docs/tutorials/testing-templates.md`: Replace `--login-type none`
example with separate Premium (`--service-account`) and OSS
(`--login-type password`) examples.
- `docs/reference/cli/users_create.md`: Regenerated from CLI source.
- `cli/testdata/coder_users_create_--help.golden`: Updated golden
snapshot.

</details>

> [!NOTE]
> Generated by Coder Agents.

cli/testdata/coder_users_create_--help.golden

@@ -19,7 +19,9 @@ OPTIONS:
           Optionally specify the login type for the user. Valid values are:
           password, none, github, oidc. Using 'none' prevents the user from
           authenticating and requires an API key/token to be generated by an
-          admin.
+          admin. Deprecated: 'none' is deprecated. Use service accounts
+          (requires Premium) for machine-to-machine access, or
+          password/github/oidc login types for regular user accounts.
 
   -p, --password string
           Specifies a password for the new user.