Github Action: Add a verification job

[matrixise]

Hi all,

Last week, I have detected some empty links, see #460. I suggest we could use the Github Actions once a week and check all the links and create an issue with the 404 links and invalidate RSS.

For that, I suggest creating a small script with aiohttp and just check all the links.

What do you think about this idea?

Thank you,

Stéphane