feat(24.10): add python3 slice

[linostar]

Proposed changes

Add python3 slice, which depends on python3.12 slices and add a couple of symlinks over that.

Related issues/PRs

N/A

Forward porting

PR #387

Checklist

• [x] I have read the contributing guidelines
• [x] I have tested my changes (see how)
• [x] I have already submitted the CLA form

Additional Context

N/A

[github-actions[bot]]

Diff of dependencies:

slices/python3-minimal.yaml

```diff @@ -1,2 +1 @@ -dpkg python3.12-minimal ```

---

[linostar]

I added python3 symlink to the python3_core and python3_standard slices.