feat(stacks): rework pages + new Jekyll tag

[Frzk]

During the work related to the release of scalingo-26 and deprecation of scalingo-22, we noticed with @benjaminach that it was sometimes "hard" to understand what exactly lies behind "supported", "deprecated" and "discontinued".

This PR aims at making this clear by:

• Featuring a section detailing the Lifecycle and the 3 statuses on the Overview page.
• Reworking the dedicated page of each stack to include the current status, and allow users to check each stack's lifecycle.
• Introducing a new Jekyll tag that adds a little icon next to the stack name, providing its current status (especially useful in the headers of the tables summarizing the supported technologies).

Tag usage (notice no - between scalingo and the number!):

{% scalingo 24 %}