Move official IRC presence to Libera

[meejah]

There have been some changes at Freenode and most ex-freenode-staff have moved to Libera. We should follow suit and move our official IRC channel to #tahoe-lafs on Libera.

People have been pro-active about granting ops etc into channels that exist on both. Other considerations:

• de-commission the Freenode presence? How?
  • keep freenode channel "alive"
  • change topic
  • nobody can post; must go to libera
• update docs to point at Libera + #tahoe-lafs instead of Freenode.
• Slack bridge should point to Libera (possibly "also point to Libera" if that's easy)

We agreed that it's also important to show support for the ex-freenode volunteers by moving to Libera. Other communications infrastructure (e.g. Zulip was mentioned, OFTC was mentioned) can be decided upon or changed later.

[exarkun]

Freenode #tahoe-lafs now has a topic pointing to irc.libera.chat and with +q set on *@*

[maylee]

Slack bridge has been asked to be pointed at Libera.

[exarkun]

Freenode #tahoe-lafs has now been re-appropriated by the new Freenode management and is no longer under our control.

[sajith]

Updated docs in PR ​1068, and it has been merged. Slack bridge has not been updated, so keeping this ticket open.

[exarkun]

Per development process (one ticket, one PR) - closing.

[meejah]

I have re-gained ops in #tahoe-lafs on freenode and changed the topic to "historic channel for Tahoe-LAFS discussion. Not allowed to point at current place of discussion."

"eskimo" in #freenode-services says you're not allowed to say "moved" and not allowed to de-voice / "close" the channel, so I guess we'll see what happens? Their suggestion was to use a bot to point people elsewhere .. but I don't want MORE infrastructure on freenode etc.