Allow user to set their own custom activation commands for the interpreter

Upon creating a terminal, an activation command to activate the current environment is sent to the terminal.

There are often issues like https://github.com/microsoft/vscode-python/issues/8770, where environment is not activated due to extension sending the wrong activation commands.

Example: An activation command used to work with conda x.x.x, but conda y.y.y changed something so it is no longer valid. And if the extension does not keep up with the change, activating the environment would fail.

Allow user to set their own activation commands for the interpreter they’re using. Often they know the correct activation commands as you can notice in https://github.com/microsoft/vscode-python/issues/8770.

[Khazbs]

Came here from #9917. There are a lot of things VSCode doesn’t do right, and activating a Python virtual environment by source-ing the activate script instead of using workon is definitely one of them. The postactivate script is just ignored. Bummer! I really hope this feature would allow us to workon our virtual environments.

[GuillaumeDesforges]

+1 Same for me with #14794, it would even allow to use Nix shell