[TSC]: Choose on a communication Platform

[ovflowd]

Right now Webpack uses a mix of Slack and Discord for both community and internal comms (and at times evne private Twitter DMs) -- We should decide upon one single communication platform, I do believe that:

• We should of course stop using Twitter DMs
• We should archive the Webpack Slack (close for new members; archive all common channels such as #general)
• Adopt Discord as the main communication platform (for community, announcements, development and internal conversation, such as TSC communication)
• Open a #webpack-core channel on OpenJS Foundation Slack so that we Foundation has a direct comm channel with us.

[evenstensberg]

I'm in favor for sentralizing to discord but slack has been a good platform for maintainers to use and we should at least have that open for feedback/conversations between teams when/if needed.