Rename whitelist to something more accurate like allowlist

Whitelist is not an accurate term for an allow_list, it's also racial stereotyping.

Let's find a new name and change it.
I suggest: allowlist

Pretty sure blacklist is not used in this module?
If it is, change that to denylist as well.

I'll try creating a patch for this if I find the time in the coming weeks.

Remaining tasks

- Update the code base (maintain backwards compatibility with whitelist?)
- Add update hook to preserve functionality (if required?)
- Update translations where necessary (if required?)

Here's an example of another module that recently made the change:
https://www.drupal.org/project/eu_cookie_compliance/issues/3150156