[Feature] Add support for footnotes in crepe

[Aurora-226]

Initial checklist

• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything (or linked relevant results below)

Affected packages and versions

“@milkdown/crepe”：“7.10.4”，“@milkdown/kit”：“7.10.4”，“@milkdown/plugin-collab”：“7.10.4”

Link to runnable example

https://milkdown.dev/playground?text=BIUwTiDkDOAFCGtoEsC2AHANiWAzA9vgC4B2xIAOgNoB6AjALoBQT19DAXLACoAWycAbCK8cuZGGhE8hUuQB0LADwAjMAAIA9AD4WQA%3D

Steps to reproduce

The manually entered footnote syntax fails to render correctly.

Expected behavior

Actual behavior

1. Unable to display footnote styles.
2. Lack of jump function.
   

Runtime

Chrome

OS

Windows

Build and bundle tools

Vite

[Saul-Mirone]

The inputrule and ux for adding footnote are not supported. But markdown contains footnotes can be parsed correctly.

https://milkdown.dev/playground?text=CoUwzgLgBA2gegRgLoCgX2QLigQSgMwHtDoA7EkNIA%3D%3D