feat: pdm venv integration

[frostming]

Pull Request Check List

• A news fragment is added in news/ describing what is new.
• Test cases added for changed code.

Describe what you have changed in this PR.

1. pdm venv commands integration

2. pdm init will ask to create virtualenv if not exists
   pdm init, when choose to create virtualenv:
   
   pdm init, when choose not to create virtualenv:
   

3. pdm use will list pythons in central virtualenv location

4. pdm install will create virtualenv if python is not chosen yet and __pypackages__ doesn't exist

5. venv will be created at .venv in project root, while configurable.

[codecov-commenter]

Codecov Report

Merging #1193 (75c9446) into main (e3e145c) will decrease coverage by 4.22%.
The diff coverage is 94.11%.

@@            Coverage Diff             @@
##             main    #1193      +/-   ##
==========================================
- Coverage   85.32%   81.09%   -4.23%     
==========================================
  Files          78       93      +15     
  Lines        6834     7592     +758     
  Branches     1565     1792     +227     
==========================================
+ Hits         5831     6157     +326     
- Misses        666     1081     +415     
- Partials      337      354      +17     

Flag	Coverage Δ
unittests	80.97% <94.11%> (-4.11%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pdm/cli/commands/plugin.py	64.28% <ø> (ø)
pdm/project/config.py	94.11% <ø> (ø)
pdm/utils.py	81.71% <ø> (+3.24%)	⬆️
pdm/project/core.py	89.29% <86.48%> (-0.03%)	⬇️
pdm/cli/commands/venv/list.py	87.50% <87.50%> (ø)
pdm/cli/commands/venv/remove.py	87.50% <87.50%> (ø)
pdm/cli/commands/init.py	98.18% <92.30%> (-1.82%)	⬇️
pdm/cli/commands/venv/purge.py	94.28% <94.28%> (ø)
pdm/cli/commands/venv/__init__.py	95.65% <95.65%> (ø)
pdm/cli/commands/venv/activate.py	96.00% <96.00%> (ø)
... and 26 more

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[thiagola92]

First, i'm loving pdm! Thank you very much!

Second, why the change to use venv by default?

Observation: Is False in configuration.md
https://github.com/pdm-project/pdm/blob/main/docs/docs/usage/configuration.md?plain=1#L20

[frostming]

@thiagola92 here are some explanations. And the doc definitely needs to be updated, would you like to contribute?