Fix and improve startup performances of Python workspaces using venv

[cccs-eric]

Describe the bug

When using a python virtual environment, the vscode-python sidecar cannot activate the venv since it tries to activate it using the source command, which is not available in the current shell (/bin/sh).

Che version

7.29.2

Steps to reproduce

1. Create a new workspace using the built-in Python stack.
2. Once the workspace is loaded, set up a new venv using the devfile's set up venv command
3. Change the Python interpreter and select the venv python3 binary under /projects/.venv/bin/python3
4. Open the hello-world.py file and execute it using the green "Play" arrow located at the top-right of the editor
5. You should see the following error:

$ source /projects/.venv/bin/activate
/bin/sh: 1: source: not found
$ /projects/.venv/bin/python3 /projects/python-hello-world/hello-world.py
Hello, world!

Expected behavior

I should be able to run hello-world.py using the devfile command and also the built-in run button of the editor. But to do so, it needs to activate the venv associated.

Not sure what would be the best solution, but I can see:

1. Change the default shell of the sidecar to be bash, so source can be used
2. Change the way the venv is activated by using . instead or source

Screenshots

Release Notes Text

The default Python image now uses bash as the default shell and venv runs successfully. The startup time of an existing workspace has been significantly reduced for the Python getting started example with an update to persist venv folder.

[ericwill]

Change the default shell of the sidecar to be bash, so source can be used

I think this is preferable. The convention is to use source (at least from what I've read).

[ericwill]

@sunix this should be handled by your current work, yes?

[sunix]

@ericwill yes this is related although I did not faced that issue. The plugin sidecar is using sh by default, but as far as I remember, the dev container was OK. i will have a look while updating the devfiles with my current work.
edit:

Open the hello-world.py file and execute it using the green "Play" arrow located at the top-right of the editor

ok so this is running it in the sidecar, it will be provided with my fix (using bash for the default user in the sidecar)

[l0rd]

@ericwill can you please review if that fix will be ported downstream (and update the new and noteworthy label if it won't)?

[ericwill]

@ericwill can you please review if that fix will be ported downstream (and update the new and noteworthy label if it won't)?

It won't be making it for 2.9 but it will make it for 2.10.