Issue #1696: Add mentors to metadata, generate mentor list automatically

[MohanadKh03]

PR Summary:

• Mentor names are extracted automatically from the GSoC proposal pages from their front matter "YAML format"
• The mentors are listed uniquely by their email on the mentors page

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[vvolkl]

This is fantastic, thank you very much for this contribution!

One small comment: names are unfortunately a bit complicated to handle, and here we have one case where the mentor has a last name and first name with whitespace. (First name: "John S." Last name: "De Stefano Jr."
I'd suggest to just add a firstname and lastname field to the yaml header, like that you don't need to split the full name.

[MohanadKh03]

I'd suggest to just add a firstname and lastname field to the yaml header, like that you don't need to split the full name.

Done

My bad I made a mistake while resolving the conflict but now it is fixed

[vvolkl]

I've added some small fixes, now this LGTM:

• mentor section in proposals from 2025 onwards. old
  projects do not have the metadata.
• add is_preferred_contact that just prints the mentor in bold
• change mentor.role to mentor.additional_information for more
  flexibility

Your work was very easy to extend, thanks again for this nice contribution!

[vvolkl]

Fixes #1696