Add VTX Temperature Export (with rebased branch)

[kaelyndunnell]

Proposed changes

Add VTX Temperature Export for HydrogenTransportProblem Class. Linked to PR #950 , but needed to rebase branch. Conflicts in branch for #950 too numerous to efficiently resolve.

Types of changes

What types of changes does your code introduce to FESTIM?

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Code refactoring
• Documentation Update (if none of the other choices apply)
• New tests

Checklist

• Black formatted
• Unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...

[RemDelaporteMathurin]

@jhdark I worked with Kaelyn on this, would you mind giving it a quick look just in case you have another idea (and to make sure it's understandable)?

[jhdark]

looks grand, just needs a rebase from the fenicsx branch