Incorporate DSL2 features into docs

[bentsherman]

This PR moves the DSL2 features (functions, workflows, modules) into the main docs, since they are well-established language features now. The DSL2 page has been refactored into a "DSL1 migration guide" so that there are still some DSL1 examples, since the rest of the docs use DSL2 now and we don't maintain docs for older versions.

The sections on functions, workflows, and modules were mostly copy/paste into their own sections, with some minor edits for clarity.

These changes should be consistent with what we were planning anyway for the website overhaul, but I decided to move forward with it now instead of wait, since the overhaul has been stalled for so long. These changes should make the docs truly DSL2-first.

[ewels]

Awesome work 👏🏻

Some minor suggested changes, though not sure of these are me commenting on the original docs that you've moved around. Big improvement though, thanks @bentsherman! 🚀

[bentsherman]

@pditommaso ready to merge?

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[bentsherman]

@pditommaso it would be good to merge this one before the 23.10 release, since DSL2 is now required, it will make the docs truly DSL2-first.

It also refactors the DSL2 page into a DSL1 migration guide, so that there is still a reference for the old DSL1 syntax, and it is geared more towards migrating old DSL1 code.

[bentsherman]

@pditommaso can we please merge this before the stable release?

[pditommaso]

I'll check asap

[pditommaso]

I cannot build this. Does it require some changes in the sphinx container?

» b make-html.sh
sphinx-build -b html -d _build/doctrees   . _build/html
Running Sphinx v5.3.0

Extension error:
Could not import extension sphinxext.rediraffe (exception: No module named 'sphinxext')
make: *** [Makefile:45: html] Error 2
Done. See _build/html/index.html

[pditommaso]

Solved! 148a34b 😎

[pditommaso]

Nice job! 👍

[ewels]