Add release drafter

[curquiza]

Will automatically create/update a release draft.

How it works:

• The release description is generated and corresponds to all the PRs titles since the previous release.
• As the description is generated on every push on master, don't change it manually until the final release publishment.
• If you don't want a PR to appear in the release: set the label skip-changelog
• If the changes you are doing on the PR are breaking: set the label breaking change. The minor instead of the patch will be increased. (The major will not change because MeiliSearch is not stable yet)
• If you forgot to add a label or if you want to change the title of a PR but the PR is already closed, don't panic: change what you want on the closed PR and run the job again.

More information about release drafter.

NB: the secret RELEASE_DRAFTER_TOKEN is set 🙂

FYI: we already use the release drafter in all the other repositories. Check this one, for example, all the releases have been generated (before being manually pushed)