feat: remove `callouts` in favor of `admonition`

Summary

Добавлено расширение admonition, позволяющее использовать выноски:

!!! note "Phasellus posuere in sem ut cursus"
    Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nulla et euismod
    nulla. Curabitur feugiat, tortor non consequat finibus, justo purus auctor
    massa, nec semper lorem quam in massa.

See:

• https://squidfunk.github.io/mkdocs-material/reference/admonitions/
• https://python-markdown.github.io/extensions/admonition/

---

• Changes should be cherry-picked to 24.2: no
• Staging: https://docs.binary.picodata.io/picodata/asabirov_set_up_admonitions/
• See also !289 (merged)