Updated developer docs

[dlcaballero16]

Updated docs to remove references to sans-backend,
removed references to ORNL dev procedures, (deleted CONTRIBUTING.rst and OnboardingChecklist.rst)
moved info from README_developer into readthedocs, (deleted README_developer.rst and put info in docs/developer/index.rst)
and changed conda steps to use pixi steps instead.

Description of work:

Check all that apply:

• updated documentation and checked that it looks correct in the pull request preview
• Source added/refactored
• Added unit tests
• Added integration tests
• Included a manual test for the reviewer
• Verified that tests requiring the /SNS and /HFIR filesystems pass without fail

References:

• Links to IBM EWM items: 14120
• Links to related issues or pull requests:

⚠️ Manual test for the reviewer

Just make sure the docs look correct.

Check list for the reviewer

• best software practices
  • clearly named variables (better to be verbose in variable names)
  • code comments explaining the intent of code blocks
• All the tests are passing
• The documentation is up to date and looks correct in the pull request preview
• code comments added when explaining intent

Execution of tests requiring the /SNS and /HFIR filesystems

It is strongly encouraged that the reviewer runs the following tests in their local machine
because these tests are not run by the GitLab CI. It is assumed that the reviewer has the /SNS and /HFIR filesystems
remotely mounted in their machine.

cd /path/to/my/local/drtsans/repo/
git fetch origin merge-requests/<MERGE_REQUEST_NUMBER>/head:mr<MERGE_REQUEST_NUMBER>
git switch mr<MERGE_REQUEST_NUMBER>
pixi shell  # activate the environment
pytest -m mount_eqsans ./tests/unit/ ./tests/integration/
exit  # exit the environment

In the above code snippet, substitute <MERGE_REQUEST_NUMBER> for the actual merge request number. Also substitute
<my_drtsans_dev_environment> with the name of the conda environment you use for development. It is critical that
you have installed the repo in this conda environment in editable mode with pip install -e . or conda develop .

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.05%. Comparing base (c18f8f2) to head (70dbccb).

Additional details and impacted files

@@           Coverage Diff           @@
##             next    #1093   +/-   ##
=======================================
  Coverage   86.05%   86.05%           
=======================================
  Files         102      102           
  Lines       11508    11508           
=======================================
  Hits         9903     9903           
  Misses       1605     1605           

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[jmborr]

👌