JP-1931: Add/Rename V2-V3 frame axes names

[mcara]

This PR changes the case of V2-V3 axes for NIRSPEC from V2->v2 and adds axes names for v2v3 frames for other instruments. This takes care of #5602 (comment) and item #4 in #5746 (comment)

This PR also fixes units for the v2v3 frame for NIRCAM (u.deg->u.arcsec) as described in item #2 in #5746 (comment).

However, I have noticed many other (than v2v3) frames also do not have axes names.

Resolves #5770 / JP-1931

[codecov]

Codecov Report

Merging #5765 (53c4e70) into master (1133e42) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #5765      +/-   ##
==========================================
+ Coverage   75.93%   75.98%   +0.04%     
==========================================
  Files         406      406              
  Lines       36135    36391     +256     
==========================================
+ Hits        27439    27650     +211     
- Misses       8696     8741      +45     

Flag	Coverage Δ		*Carryforward flag
nightly	75.93% <100.00%> (ø)		Carriedforward from 1133e42
unit	54.61% <87.50%> (ø)

*This pull request uses carry forward flags. Click here to find out more.

Impacted Files	Coverage Δ
jwst/assign_wcs/fgs.py	72.22% <100.00%> (-22.65%)	⬇️
jwst/assign_wcs/miri.py	87.08% <100.00%> (-2.88%)	⬇️
jwst/assign_wcs/nircam.py	88.67% <100.00%> (+0.32%)	⬆️
jwst/assign_wcs/niriss.py	80.10% <100.00%> (+2.98%)	⬆️
jwst/assign_wcs/nirspec.py	93.91% <100.00%> (ø)
jwst/group_scale/group_scale.py	100.00% <100.00%> (ø)
jwst/group_scale/group_scale_step.py	100.00% <100.00%> (ø)
... and 2 more

---

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[jdavies-st]

Looks good. Just add an entry to CHANGES.rst

[nden]

lgtm

[mcara]

I do not understand how can code coverage change after this PR. It is just renaming things.

[jdavies-st]

Codecov seems to be having some technical difficulties right now.