Doc/Michelson: redirect never and string operations to interactive reference

Context

Answers this part of #4077:

• delete the parts about instructions from the static reference:
  • Operations on type never
  • Operations on strings

The documentation about all the operations on never and string in the interactive reference contains that found in the static reference, except for the description of the string type, which is completed in michelson-reference!75 (merged).
The inclusion was checked manually by comparing the static and interactive documentations for each type and comparison instruction of the static reference.

Manually testing the MR

make -C docs -j

And then open docs/_build/alpha/michelson.html in a web browser.

Or open the exposed artifacts Documentation - excluding old protocols below, and navigate to docs/_build/alpha/michelson.html.

Checklist

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