update documentation for deprecated matplotlib references

[yusufjimoh]

Description of work

Summary of work

update deprecated matplotlib references in mantid documentation to the latest

Fixes #37603.

To test:

Build the docs-html target and check that the changes render correctly

This does not require release notes because it is only a documentation update.

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[rbauststfc]

Looks like a really thorough update of all the relevant URLs. I've built both the user and dev docs and the changes are rendering well with all the new links working.

I noticed a very small typo that is unrelated to these changes but might be good to fix while we're here, if that's OK.

The other thing that might just be good to discuss quickly with the Core team (if you haven't already) is that I think at the moment we're on Matplotlib 3.7. Despina is working on #38077 to move us to 3.8. The current stable version is 3.9. I've noticed that a lot of the URL updates in this PR are pointing us to the docs for the stable version. The benefit of not specifying the version in the links is obviously that they won't need updating every time we update Matplotlib, but there is a small risk that we're pointing to documentation that isn't totally accurate for the version we're on. Might be good to just get a second opinion from Core to confirm we're happy with this.

[rbauststfc]

Sorry, this isn't part of your changes, but while we're here could we fix the typo in the spelling of the word "available" here?