[4.0.0 future major release] Drop Python 2 support

[Andersson007]

SUMMARY

[4.0.0 future major release] Drop Python 2 support on target hosts as ansible-core 2.16 (the last version that requires it) gets EOL in May 2025.

• Announce it under breaking_changes
• Stop testing the main branch against it
• Start accepting new features written in Python 3 (bugfixes will still must be compatible with Python 2 as they'll get backported to stable-3)

Any concerns/random thoughts/approvals, folks?