JP-3525: Merge jump and ramp_fitting docs content with jwst docs

[hbushouse]

This PR partially resolves JP-3525 by making updates to the docs stored in stcal, in order to merge and sort out the info between the docs in jwst and stcal. Related updates will be made in jwst/docs. The vast majority of the high-level step information, especially those things that are JWST-specific, is being moved to jwst/docs, while the stcal/docs retain only low-level algorithmic information.

Checklist

• [x] added entry in CHANGES.rst (either in Bug Fixes or Changes to API)
• [ ] updated relevant tests
• [x] updated relevant documentation
• [ ] updated relevant milestone(s)
• [x] added relevant label(s)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (fd2d6ce) 85.98% compared to head (bc5f5e8) 85.98%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #240 +/- ## ======================================= Coverage 85.98% 85.98% ======================================= Files 35 35 Lines 6542 6542 ======================================= Hits 5625 5625 Misses 917 917 ```

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[hbushouse]

I understand the hierarchy and linking of the documentation for the different repos is difficult, but much of the documentation being removed from the STCAL repo is about how ramp fitting works in STCAL. In the future, if someone wants to use STCAL for a new telescope, they need to know the information in the documentation being deleted.

I thought about this some more and decided to move a lot more of the basic content from jwst to stcal, with a lot more links/references from the jwst side.