Frontpage should reflect FOSS4G-EU 2025

[justb4]

See https://dive.pygeoapi.io/ . Should show workshop providers Mostar 2025.

[justb4]

So also here, I added @geographika and @pvgenuchten as well, who else (@ldesousa ?). Or ready @tomkralidis ?
Edit in branch directly via:
https://github.com/geopython/diving-into-pygeoapi/blob/200-frontpage-team/workshop/content/docs/index.md

[tomkralidis]

Thanks @justb4. I'll merge for now (added an update for the conclusion page), and wait for feedback from @ldesousa