Replace mypy_integration_config repo with label flag

[UebelAndre]

Currently the mypy.ini config file is determined via a repository. This can lead to issues where one repository does not define this or two repositories attempt to create it using different config files. Instead of having users add the following in their workspace

load("//:config.bzl", "mypy_configuration")

mypy_configuration()

This PR has them update their .bazelrc files to pass a build flag which defines what config to use

build --@mypy_integration//:mypy_config=//:mypy.ini

In this case, a mypy.ini in the root of the current workspace would be used as the mypy config.

[ianoc]

Wouldn't a toolchain be the more usual way to configure a global setting like this, any reason to use a setting here instead?

[UebelAndre]

Wouldn't a toolchain be the more usual way to configure a global setting like this, any reason to use a setting here instead?

These rules currently do not have a toolchain implemented. I think a toolchain would be fine but in the absence of all that plumbing, a global setting like this feels like the most effective step forward.

[ianoc]

Yeah fair enough, just seems like maybe a toolchain is the more expected manner than a setting was my only thought. But it does seem better. Sorry I was mostly just drive by curious why one would go with the setting, the overhead/boilerplate is a decent answer. ty!

[UebelAndre]

@alexeagle do you have time sometime in the next week or so to review this?

[UebelAndre]

@thundergolfer would you maybe be able to take a look? 🙏

[alexeagle]

Looks like an improvement to me, thanks!

[UebelAndre]

Looks like an improvement to me, thanks!

@alexeagle Thanks! Would it be possible to get a new release for this change?