Refactor tools/launchdev.sh to use tmux

[cognifloyd]

This is primarily work by @nzlosh who figured out how to replace screen with tmux in #6157. On top of that, I:

• reverted a port change in launchdev.sh that looks like copy pasta,
• added a sleep to avoid polluting so many logs with "mongo document already exists" errors as st2 processes started nearly in parallel and then attempt to initialize the database in parallel,
• refactored a few messages in launchdev.sh,
• finished cleaning up some other files to finish removing screen, and
• adjusted logs capture in GitHub Actions to be more reliable and to prevent one test from overwriting the logs of other tests.

Some of my changes were extracted from #6130.