Fixes https://github.com/certbot/certbot/issues/8781.
This PR makes our test farm tests into a normal package so it and its dependencies can be tracked and installed like our other packages.
Other noteworthy changes in this PR:
* Rather than continuing to place logs in your CWD, they're placed in a temporary directory that is printed to the terminal.
* `tests/letstest/auto_targets.yaml` was deleted rather than renamed because the file is no longer used.
* make a letstest package
* remove deleted deps
* fix letstest install
* add __init__.py
* call main
* Explicitly mention activating venv
* rerename file
* fix version.py path
* clarify "this"
* Use >= instead of caret requirement
