Add CPO main postprocessor

[MFraters]

This pull request adds a post-processor to output relevant CPO information.

This implementation is based on #4978, so this should not be merged until that one is. It is ready for review though.

(point 3 in #3885)

[MFraters]

Now that #4978 is merged, I have rebased this pull request to the current main branch. It should now be fully ready.

[MFraters]

Just for my understanding: Is this essentially a copy of the particle postprocessor, except it does only process the CPO particle properties in a special way before outputting these postprocessed quantities into files that are separate from the normal particle output files?

Yes, that is correct. It allows for a flexible way to output the data in the way you want, both raw (which can be useful to look directly at the data) and volume weighted (which you need for useful pole figures). And these files can than be for example used directly to make these pole figures with this code: https://github.com/mfraters/cpo_analyzer.

[MFraters]

Thanks for the review! I have addressed your initial comments :)

[MFraters]

I have updated this pull request after #5094 got merged. See comment in #4980 about tests

[MFraters]

Thanks for the review. I have adressed all your comments and it i ready for another review :)

[MFraters]

Thanks for the review. I have addressed your comments.

[MFraters]

Thanks, I have addressed your comments.

[MFraters]

Fixed the changlog entry