Update Note and Warning markdown highlighting with GitHub's changes

[yardenshoham]

Feature Description

Since July 21st, GitHub has made a few changes to their feature. We introduced it into Gitea with #21711. Now we need to update the implementation to match GitHub's, including a syntax change. An example of the current implementation on GitHub:

Note

Highlights information that users should take into account, even when skimming.

Tip

Optional information to help a user be more successful.

Important

Crucial information necessary for users to succeed.

Warning

Critical content demanding immediate user attention due to potential risks.

Caution

Negative potential consequences of an action.

Docs: https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#alerts https://github.com/orgs/community/discussions/16925

Screenshots

No response

[lng2020]

So, If I understand correctly, GitHub no longer supports

>**NOTE**
>something

Instead, it uses

>[!NOTE]  
>something

That's a breaking change. Should we follow what GitHub did?

[yardenshoham]

I think we should follow GitHub on this feature

[github-actions]

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