Update who-is-who.md

[mb-david-cajal]

Description

This PR updates the "Who is who" and "Information Security Management" sections of the company handbook to reflect recent team changes, fix formatting, and add social profiles.

Changes made

• Head of People update: Set Eli as the sole Head of People for now and removed all references to Leire (to be re-added upon her return).
• Team roster cleanup: Removed former team members (Mateo, Juan Pablo, and Víctor) from the Engineers section.
• LinkedIn integration: Added exact LinkedIn profile links for all current team members. Following best practices, links are only included on their first occurrence to avoid cluttering the text.
• David & David distinction: Properly linked David Gómez under Engineers and David Cajal under Marketer & Podcast Co-Host.
• Formatting fixes: Replaced all em-dashes (—) with colons (:) or standard hyphens (-) to ensure clean rendering and consistency across all markdown parsers.

Checklist

• Verified all new LinkedIn URLs are correct.
• No substantial text descriptions were modified.
• References to Leire removed completely.

Reason for change

Closes # .

List of Changes

• Describe your changes as a concise list of items.
• This should be more informative than the diff itself.

Checklist

• I have updated necessary documentation and links in the README.md or the doc folder
• I have rebased from main, written good commit messages and squashed unnecessary commits

[alexrodba]

All good, just need to add Marta as tech lead too @mb-david-cajal and we can merge this