FIREFLY-1862: Cleanup the firefly-client docs and example notebooks

[jaladh-singhal]

Fixes FIREFLY-1862

• Restructured examples/ contents: added meaningful names/titles, merged/deleted duplicate notebooks, moved deprecated and testing notebooks to a sub directory, etc.
  • test/ directory has now become examples/development_tests since that's what they are, they are not unit tests but integration tests in form of notebooks or scripts
• Made examples/ (all notebooks and scripts, except those in subdirectories) render as html pages in the docs website for easy view and download by user
  • This required changes in conf.py and adding a custom extension script_pages.py - we can get rid it when improving infrastructure to use myst-nb instead of nbsphinx (notebook->HTML renderer libraries) similar to https://github.com/Caltech-IPAC/irsa-tutorials
• Converted most of docs/usage/*.rst which were outdated to .ipynb files with up-to-date API usage
  • this makes it easy to test/maintain them. Eventually, we can setup a CI pipeline to test notebook code with pytest (what https://github.com/Caltech-IPAC/irsa-tutorials does)
• Fixed bugs/docstrings in firefly_client.py
• Updated publish doc workflow to build html docs for PR branches too
• Updated dev docs, demo-notebooks page, landing page, etc

Testing

See docs built from this PR-branch at https://caltech-ipac.github.io/firefly_client/pr/76/

Compare them against current docs (built from master branch): https://caltech-ipac.github.io/firefly_client/

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[robyww]

@jaladh-singhal gave me an overview. It looks good.

[stargaser]

I only looked at a few parts, but it looks good to me.