Introduce guide when RLS notes missing

## Background

- Creating release notes (title and bullet list) requires manual effort or relies on PR templates. In both cases, the PR author needs to pay extra attention and follow a process that can be repetitive.
- To improve the developer experience and reduce time spent on boilerplate work, the action will offer two optional inputs to automate or assist with release notes creation.

## Feature

Introduce two new inputs:

### `guide`
- **Required**: No
- **Default**: `true`
- **Description**:
When enabled and no "Release Notes" section is found in the PR description, the action will post a helpful guide comment.
The comment includes:
- A short explanation + mention automated injection feature
- A release notes template
- A proposed draft generated from commit messages

This serves as a non-intrusive way to guide contributors.
If a guide comment from the action already exists, it won’t be posted again.

> 🔹 If both `guide` and `inject_proposed_draft` are enabled, the guide comment is **skipped** to avoid redundancy.

---

### `inject_proposed_draft`
- **Required**: No
- **Default**: `false`
- **Description**:
When enabled, the action will directly insert the generated release notes draft into the PR description.
This provides a ready-to-edit section based on commit messages, saving the author time.

> 🔸 This takes precedence over the `guide` input. When both are enabled, the guide comment will not be posted.