Add everest-models as a package installation when building readthedocs for everest

[DanSava]

Issue
Resolves #9930

Approach
Add everest-models as a package installation when building readthedocs for everest

(Screenshot of new behavior in GUI if applicable)

• PR title captures the intent of the changes, and is fitting for release notes.
• Added appropriate release note label
• Commit history is consistent and clean, in line with the contribution guidelines.
• Make sure unit tests pass locally after every commit (git rebase -i main --exec 'just rapid-tests')

When applicable

• When there are user facing changes: Updated documentation
• New behavior or changes to existing untested code: Ensured that unit tests are added (See Ground Rules).
• Large PR: Prepare changes in small commits for more convenient review
• Bug fix: Add regression test for the bug
• Bug fix: Create Backport PR to latest release

[codspeed-hq]

CodSpeed Performance Report

Merging #9940 will not alter performance

_{Comparing DanSava:fix-readthedocs-everest (da3d3b8) with main (7c27a9c)}

Summary

✅ 25 untouched benchmarks

[yngve-sk]

LGTM, tested building docs and it seems to work on my machine