[DOC] add link to bluesky account instead of twitter

[jeromedockes]

Ping @rcap107 who has become our official social media / PR person despite himself 😝

[rcap107]

"volunteered"

Not sure if we should replace the icon entirely, or keep both bsky and twitter, @GaelVaroquaux what do you think?

[jeromedockes]

note the pydata sphinx theme does not seem to like more than 2 icons -- but we already have that problem with the current number of links

[Vincent-Maladiere]

What happens if we have 4 icons? I'm slightly uncomfortable leaving Twitter entirely, some people could see a politically motivated move