[Feature request] allow config gray-matter setting

[bluelovers]

Feature request

i wanna parse other format 's front matter

but this looks like is close config , no way change it
https://github.com/vuejs/vuepress/blob/master/packages/@vuepress/shared-utils/src/parseFrontmatter.ts

What problem does this feature solve?

can parse other format

What does the proposed API look like?

same as gray-matter

How should this be implemented in your opinion?

Are you willing to work on this yourself?

if take this idea, i can try , but im 0% understand vuepress code

[MartinMuzatko]

This would be great!

Vuepress is first parsing the markdown file for --- and then finally passing that to gray-matter.
https://github.com/vuejs/vuepress/blob/master/packages/@vuepress/shared-utils/src/parseVueFrontmatter.ts#L6
and passes to:
https://github.com/vuejs/vuepress/blob/master/packages/@vuepress/shared-utils/src/parseFrontmatter.ts