Add option to specify junit xml testsuite name

[dyollb]

Feature

Add an option to specify junit xml testsuite name. For example --junit-xml-name or --junit-suite-name .

Pitch

Currently, mypy just writes the generic testsuite name "mypy". In a CI with multiple mypy invocations, this is not specific enough to quickly get an overview of which package is failing.

[wyattscarpenter]

I don't know enough about junit workflows to comment, but I thought I'd mention that if we add any more junit options we should give junit its own config section instead of just having its options live in misc. (Which is not a downside.)

Also, while I don't myself know if it has any merit, this new flag seems like it would be quite easy to make, based on my interactions with the relevant subsystems. A simple option to add.