Clarify whether `ignore-project: True` also ignores `cabal.project.local/freeze`

Currently, it is stated that `ignore-project: True` (only?) ignores `cabal.project`:
https://github.com/haskell/cabal/blob/a97e1f13bdb28a3f761d55845f14a9072bee17ca/doc/cabal-project.rst#L306-L309
However, since `--project-file` also affects the `.local` and `.freeze` variants, it would be good to be explicit here: Either say that the local/freeze files are _not_ ignored, or that they are _also_ ignored.

Read the `ignore-project` documentation in `doc/cabal-project.rst` at the linked section, then inspect how `--project-file` handles the `.local` and `.freeze` variants. Clarify the documentation to state whether those variants are ignored, and ensure the wording matches the actual behavior.

Written by the indexing model from the issue text.