Update walk through and user guides

[elliotgunton]

Pull Request Checklist

• Fixes Walk-through documentation updates #1273
• Tests added Docs only
• Documentation/examples added
• Good commit messages and/or PR title

Description of PR
Main changes:

• Surface the "hera developer features" walk through section in the walk through
  before the "authentication" section so users start seeing Hera's unique features
  earlier
  • Added the "Set class defaults" section here
• Separate out the experimental features into its own section as it's big enough
• Rename the "advanced features" section to "further reading" to be less scary
• Remove the under-utilised Pydantic integration section, move relevant
  sections of text to the user guides - new "Integrated Pydantic Support" section
  in script-basics.md for the RunnerScriptConstructor
• Add more motivation to the Runner IO to make it more obvious why it's needed

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.2%. Comparing base (93da5f1) to head (2611c69).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #1288   +/-   ##
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  Coverage   86.2%   86.2%           
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  Files         60      60           
  Lines       4091    4091           
  Branches     653     653           
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  Hits        3530    3530           
  Misses       391     391           
  Partials     170     170           

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[alicederyn]

Should this maybe be under "Further Reading"?

[elliotgunton]

I think it's important enough to be top-level in the walkthrough as it tells users about actively developed features. I think it might make sense to just leave the intro paragraph and move the rest to a new "user guide".

I actually wanted to avoid having a "further reading" section because that completely hides the sections and information when opening the page, but the workflow/template features in there aren't really needed in a walkthrough/intro to Hera.

[alicederyn]

🚀