Collect Mattermost security updates

[pombredanne]

See https://mattermost.com/security-updates/

[Pushpit07]

Do you mean that the data here in this screenshot is to be scraped?

[prathamaror]

can i start working on this?

[Hritik14]

The work was partial, this needs to be refactored and migrated to importer improver structure

[armijnhemel]

It might be more useful to subscribe to the security mailing list instead of scraping the webpage.

[TG1999]

dependent on aboutcode-org/univers#97