Allow `--force` activate `poetry shell` when poetry fails to activate it

• I am on the latest Poetry version.

• I have searched the issues of this repo and believe that this is not a duplicate.

• If an exception occurs when executing a command, I executed it again in debug mode (-vvv option).

• OS version and name: Ubuntu 20.04

• Poetry version: 1.1.13

Issue

Often times poetry keeps thinking I have a shell already activated, and I don't. This is widely reported by others too (#4622, python-poetry/poetry-plugin-shell#21, python-poetry/poetry#5050, python-poetry/poetry#3136). I also do not have any conda environment activated (not even base). In this case, I am just forced to use the full path to the venv to run the activate script manually. I propose that we should be able to do this in poetry, when it inevitable fails to activate the venv, to --force activate the environment, so that even if it is "already active" (not actually), it will still be "activated" (for the first time).

Current output

$ poetry shell -vvv
Using virtualenv: ...-py3.8
Virtual environment already activated: ...-py3.8

Proposed Usage example:

$ poetry shell
Virtual environment already activated: ...

$ poetry shell -f
Force-activating Virtual environment: ...

Start with the poetry shell command and reproduce the reported Virtual environment already activated output on Ubuntu. Trace the existing activation decision and define completion as a force option that activates the environment despite that detection, with output matching the proposed usage example.