Replace old Breeze with Python based implementation

[potiuk]

Over the last few months together with Outreachy interns
we rewrote the most important functionality of the old Bash-based
Breeze with Python Based implementation.

We approached it in systematic way with capturing all our decisions
in the ADR format (dev/breeze/docs) and implementing the parts
that are used on a daily basis by the users. Breeze2 as it was
called is ready for Prime-Time with the users so we are swapping
out the old breeze wiht the new one.

The old breeze has been moved to breeze-legacy and we will
gradually parts of it that are already migrated to Python and proven
while continue rewriting the parts that are missing (mostly the
maintainer tools) and replacing the remaining CI shell scripts with
the new breeze commands.

We also need to make sure that there is no accidental top-level
import for extra packages added in the future, because people
who installed breeze before will not have it - so we have
a pre-commit that checks if breeze.py can be parsed and
--help executed with just rich and click installed.

This PR:

• moves breeze to breeze-legacy
• moves Breeze2 to breeze
• updates documentation and screenshots where applicable
• explains old vs. new breeze in documentation
• adds protection so that no accidental top-level import is
  added to breeze.py and files imported from there

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[potiuk]

cc: @Bowrna @edithturn

[potiuk]

Here it is.

Switching to Python based Breeze. FINALLY.

Note. I would like to drag your attention to this nicely generated screenshots in our Breeze documentation :) https://github.com/potiuk/airflow/blob/swap-old-breeze-with-new/BREEZE.rst#installation

[edithturn]

@potiuk I ran it on my machine (Linux Ubuntu 20.10), wow works very nice! That part of the comments with a click is fantastic 🤩

I ran some commands like "config" and "start-airflow". My question is if all these options al already implemented.

• In config, I got no output or a warning saying that we set Python as a backend. (Maybe I don't understand exactly how is its behavior)
• I also ran, start-airflow, and tmux session is being open on my VSC terminal, (this is so nice 👏🏼 ), my question is in the part of creating permissions (four windows). Am I doing something wrong to get that error? or I should do an extra step to have it configure it
  

It is fantastic @potiuk and also is 💯 faster on my computer 👏🏼 🚀

[potiuk]

• In config, I got no output or a warning saying that we set Python as a backend. (Maybe I don't understand exactly how is its behavior)

Good Point. We should give feedback to the user ! The idea is that when you set python version, next time you get that default python version when you do not specify any python version. I.e. .

breeze -> Python 3.7 used by default
breeze config --python 3.8 -> python 3.8 set as default
breeze -> Python 3.8 used

I also ran, start-airflow, and tmux session is being open on my VSC terminal, (this is so nice 👏🏼 ), my question is in the part of creating permissions (four windows). Am I doing something wrong to get that error? or I should do an extra step to have it configure it

The errors are unrelated - they are also with current breeze' start-airflow - I will raise that to others as we are very close to cutting 2.3 branch I think those errors need to be fixed before.

[potiuk]

Config now is more "obvious". It also prints summary of the config (@edithturn ):

[potiuk]

I've also added protection to not add accidentally new top-level imports in breeze.py as they would break auto-complete and self-upgrade.

[Bowrna]

@potiuk this is amazing :) you have made this change very quickly 👍

[potiuk]

Looks like Green and ready for Python's Breeze prime time!

[edithturn]

Go ahead @potiuk, let us know! 🚀 💪🏼

[potiuk]

Hey @eladkal :). That's IT..

[eladkal]

🎉

[github-actions]

The PR most likely needs to run full matrix of tests because it modifies parts of the core of Airflow. However, committers might decide to merge it quickly and take the risk. If they don't merge it quickly - please rebase it to the latest main at your convenience, or amend the last commit of the PR, and push it with --force-with-lease.