[Feature Request]: Support GH's Markdown alerts' syntax

### Prerequisites

- [x] I have searched existing issues to ensure this feature hasn't already been requested
- [x] I have tested using the latest version of docs-builder

### What problem are you trying to solve?

Would it be possible for our docs system to support [GH's Markdown alerts](https://docs.github.com/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#alerts)?
Here's an example of how it renders today in [our docs system](https://docs.elastic.dev/kibana-dev-docs/tutorials/feature-flags-service#dynamic-config) and [in GH](https://github.com/elastic/kibana/blob/main/src/core/packages/feature-flags/README.mdx#dynamic-config).

I learned that `Myst` is supported where those alerts are written as `:::{note}` instead of `> [!NOTE]`, however, since Kibana is a public repo, writing markdowns with broken formatting (according to GH) feels wrong.

Differences:

*Myst*

```markdown
:::{warning}
This is a warning.
:::
```

*GH Alerts syntax*

```markdown
> [!WARNING]
> This is a warning.
```

### Proposed Solution

Add support for the [GH Alerts syntax](https://docs.github.com/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#alerts)

### Examples and Research

_No response_

### Alternative Solutions

_No response_

### Additional Context

_No response_

### How important is this feature to you?

Nice to have