[FEAT] Update the Hacktoberfest demo to introduce the theme for year 2022

[tbouffard]

Is your feature request related to a problem? Please describe.
Last year we introduce a way to display both the 2020 and 2021 themes: #241 and #242.
Let's add a new theme to advertise the 2022 event.

Describe the solution you'd like
Use the colors of the 2022 events as much as possible.
To do that, open https://hacktoberfest.com, and use the inspection of the page code from your browser to get the colors of the page. This year, the brand guidelines are available at https://do.co/hacktoberbrand (in a Figma)

Tasks

• update the preview image displayed in the HTML home page: [FEAT] Add the new "2022" theme in the Hacktoberfest demo #400

For other improvements, see #456.

Notes: a task that was originally planned has been moved to #556