Fix inconsistent exceptions raised with no rich installed

[akihironitta]

What does this PR do?

Found by @carmocca in #11217.

• Makes sure to raise ModuleNotFoundError if rich isn't installed or supported version of it isn't installed.
• Changes the tests so that the death tests above run regardless of rich availability.

Does your PR introduce any breaking changes? If yes, please list them.

• raise ModuleNotFoundError instead of MisconfigurationException when rich isn't installed.

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cc @SeanNaren @kaushikb11 @Borda

[carmocca]

Thanks for taking care of opening a PR.

This wasn't caught before because these tests don't really run, all jobs seem to install rich

[kaushikb11]

Thanks @akihironitta for looking into this!

[akihironitta]

Referred to the following mock 😉 :
https://github.com/PyTorchLightning/pytorch-lightning/blob/06b8f82b8a97e7e5653486731751521478f58cce/tests/plugins/test_amp_plugins.py#L252-L255