Migrate pub.dev acc to a Service Account

[marandaneto]

https://dart.dev/tools/pub/automated-publishing#publish-from-anywhere-using-a-service-account

Back then pub.dev didn't support service accounts but now it does.
We already ran into issues twice+ because we're using a personal token that expires and the only way is to either rotate the token manually or do clicks, which requires checking some stuff manually (only very few people can do that actually because of permissions), this should be solved by service accounts.

[marandaneto]

@kahest can you add the dart label? I don't have permission otherwise it won't be in our project.

[kahest]

@kahest can you add the dart label? I don't have permission otherwise it won't be in our project.

I also don't have the permission