Suppress RUF100 (unused noa) if we see a PGH004 (blanket noqa) error?

This is potentially a very niche request, but I was wondering if there was a way to suppress RUF100 errors for blanket noqa when PGH004 is enabled (and `external` lints are on)?

Right now, we live in a monorepo with flake8 configured along with our particular sub-codebase's `ruff` linting. The monorepo wide linting also comes with some company-specific error codes that we use the [`external`](https://docs.astral.sh/ruff/settings/#external) setting for. Unfortunately, we're hitting a problem with blanket noqas -- things like:

```
some_code_that_triggers_internal_lint # noqa
```

which triggers RUF100 when the *real* problem is that it should be annotated with `# noqa: `. I was hoping to use `PGH004` instead to flag these blanket noqa, but am running into two problems:

* Such errors will trigger two lints (unnecessary noqa and needs a specific error code). This is a little confusing, b/c the error code is actually the one users should pay attention to.
* The RUF100 autofix will delete the `# noqa`, even when it's necessary to silence the monorepo wide flake8.

I think the two things that'd help us with the ruff roll out are to:

* Change the RUF100 to be an unsafe-fix for blanket noqa if `external` is specified
* If PGH004 *and* RUF100 both trigger on the same noqa, only emit the PGH004 lint error (maybe hidden behind some flag)?

Would that make sense? Not sure if this is a reasonable thing to support our if our setup is too idiosyncratic.

Start by reproducing the interaction between PGH004, RUF100, blanket noqa comments, and the external setting in a minimal Ruff configuration. Compare the emitted diagnostics and RUF100 autofix behavior; done means the requested suppression or safer-fix behavior is defined and works without removing noqa comments needed for external lints.

Written by the indexing model from the issue text.