Add UGM 2024 logos

[jennaswa]

As we move towards publishing a new web page for UGM 2024 (MDAnalysis/MDAnalysis.github.io#349), it'd be great to add an updated logo(s).

@richardjgowers - Would you be able to easily update the logo you made for last year's UGM (https://github.com/MDAnalysis/branding/blob/main/logos/mdanalysis-ugm.png)?

@fiona-naughton - Looking forward to seeing what the London cats get up to! Making calls in phone booths? Hanging out at Big Ben? Riding the London Eye? The possibilities are endless!