[`flake8-builtins`] Update documentation (`A005`) (#16097)
Follow-up to https://github.com/astral-sh/ruff/pull/15951 to update
* the options links in A005 to reference
`lint.flake8-builtins.builtins-strict-checking`
* the description of the rule to explain strict vs non-strict checking
* the option documentation to point back to the rule
