Add GitHub actions

[fdodino]

Replacing Travis 🤮 by Github Actions.

• 📜 New page on the wiki was added
• 📜 Also updated Releasing page
• ⚠️ Current installation doesn't update automatically wollok-cli & wollok-site repositories, but it creates a new branch in order to create a manual PR, using a more conservative approach. Tried to use gh cli, but it still does not work with SSH (it uses machine users instead of the github action user)
• ⌚ Using the cache results in a ~6 minutes build