[FIX] core; base: lots of docstrings

* add configuration for `flake8[flake8-rst-docstring]`
* enable docstring-related checks
* fix invalid docstrings in odoo's core & `base`
* fix a few more bits (mostly missing or incorrect `:param:` info
  fields) are out of scope for the lint but my editor catches

closes odoo/odoo#74604

Signed-off-by: Xavier Morel (xmo) <xmo@odoo.com>