Added towncrier as a github workflow

[kc611]

As titled,

This PR adds towncrier as a Github workflow to check release notes for every PR. The action is intended to fail if there's no new release note, or skipped if there's a skip_release_notes label.

[kc611]

These are the default categories of changes provided by towncrier.
(https://towncrier.readthedocs.io/en/stable/tutorial.html#creating-news-fragments)

cc @numba/fpoc; We should be putting together a custom category list of changes that are to be reflected in the auto-generated release notes.

[kc611]

Made the following list of categories adapted from NumPy:

* ``highlight``: Adds a highlight bullet point to use as a possibly highlight
  of the release.
* ``np_support``: Addition of new NumPy functionality.
* ``deprecation``: Changes existing code to emit a DeprecationWarning.
* ``expired``: Removal of a deprecated part of the API.
* ``compatibility``: A change which requires users to change code and is not
  backwards compatible. (Not to be used for removal of deprecated features.)
* ``cuda``: Changes in the CUDA API.
* ``new_feature``: New user facing features like ``kwargs``.
* ``improvement``: General improvements and edge-case changes which are
  not new features or compatibility related.
* ``performance``: Performance changes that should not affect other behaviour.
* ``change``: Other changes
* ``doc``: Documentation Changes
* ``infrastructure``: Infrastructure related changes.
* ``bug_fix``: Any kind of bug fixes.

[stuartarchibald]

@kc611 Suggest raising this at the next maintainer/triage meeting to make sure that this list acceptable to all maintainers, also think that the general form of the release notes needs a general discussion/acceptance from the same group.

[apmasell]

Looking most at GitHub Actions

[stuartarchibald]

Thanks for working on this @kc611, this should help with automating the release process. I've not looked at the GHA workflows as @apmasell has done so (thanks @apmasell!). I've also not tested this manually. I have however reviewed the remaining content, most of the suggestions are minor things, but as noted in another comment, I suggest raising this PR for discussion at development meetings next week so as to ensure other interested parties are aware and have the opportunity to comment. Thanks again!

[stuartarchibald]

I think that this should be a comment in a style compliant with

numba/LICENSES.third-party

Lines 454 to 461 in e7a1e83

	NumPy (https://github.com/numpy/numpy)
	--------------------------------------
	Numba source code that references URLs starting with:
	https://github.com/numpy/numpy
	relates to use of/inclusion of/derivate work based on NumPy source code which
	has the following license:

?

[sklam]

The numpy license is a BSD-3 not MIT. If the NumPy changelog readme has a different license, please attach a link to it.

[sklam]

Comments that need addressing:

• MIT license?
• Update docs

[esc]

@sklam are you happy with the changes from b3edecb ? -- if yes, can you approve this PR, plz, thank you.

addressed