Fix <Modal.Footer> type

[Calvein]

There is no reason for them to be string, and we already pass components in some internal projects, so ReactNode should be better.

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[theo-mesnil]

@Calvein it's for translation component ?

[Calvein]

Not in the cases I just fixed, it was something like:

<Box>
  <FormattedMessage />
  <Link />
</Box>

[theo-mesnil]

@Calvein it's a custom footer, i think you need a custom footer too ? We have done this to avoid custom style on footer

[Calvein]

I think you're right, we have a weird mix which is, I'm guessing, due to the migration to the v5, I'll fix it, thanks!