Serverless flex compatibility

[c33s]

as flex is now serverless https://symfony.com/blog/symfony-flex-is-going-serverless there are some changes to the data format:

[LogicException]
  The Flex index is missing a "splits" entry. Did you forget to add "flex:[//defaults](vector://defaults/)" in the "extra.symfony.endpoint" array of your composer.json?

also the official endpoint https://symfony.sh/flex.symfony.com is now gone.

edit:

• https://symfony.com/blog/upgrade-flex-on-your-symfony-projects
• https://symfony.com/blog/symfony-flex-is-going-serverless
• https://www.reddit.com/r/symfony/comments/tavy25/the_flex_server_is_shutting_down_soon_update/
• composer update: Undefined index: splits symfony/flex#890

[sonnymilton]

https://github.com/sonnymilton/flexhub
New project compatible with Flex Serverless