Reclassify some tutorials

[abbycross]

Closes #4267

@nathanearnestnoble FYI - we discussed at QDC but confirming we're good to move these over to Guides? Also, do you have a suggestion for a renaming of Intro to fractional gates, and will it stay as a tutorial or get moved?
@kaelynj Check the toc and let me know if these new entries should get moved.

• still unresolved: Where to put Qiskit AI-powered transpiler tutorial

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One or more of the following people are relevant to this code:

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[nathanearnestnoble]

Definitely good to move "Hello world" and "Compare transpiler settings to documentation". Will open an issue to rename fractional gate tutorial.

Let me review "Combine error mitigation" and the AI transpiler and get back to you asap!

[Eric-Arellano]

Please make sure we have redirects set up before merging this for the tutorials that are moving.

[abbycross]

In this PR I've moved Hello world, Compare transpiler settings, and Combine error mitigation settings (which I am now remembering that @nathanearnestnoble said he will review this one - so just let me know if I should move it back! Sorry, holiday break brain!).
@kaelynj please review the guides toc to make sure things have landed where you would expect.
Once this is all squared, we will need the following redirects:

• tutorials/hello-world to guides/hello-world
• tutorials/circuit-transpilation-settings to guides/circuit-transpilation-settings
• tutorials/combine-error-mitigation-techniques to guides/combine-error-mitigation-techniques (if Nate says we're moving it)