Fix bad and outdated links

[bmmpxf]

A few documentation links were pointing to the old structure, and a few were 404ing. This PR fixes them.

[bmmpxf]

FYI, I'm seeing that there's a GitHub action that builds the docs on GitBook. We're no longer using GitBook, so those actions can be turned off. (Not sure who handles that.)

[jessicadaugherty]

I have tested all updated URLs to confirm they resolve to the intended host. Will check on disabling the Gitbook hooks.

[jessicadaugherty]

Update on Gitbook integration: disabling requires account owner to 2FA so will need to figure that out before removing it from this workflow @bmmpxf

[bmmpxf]

Update on Gitbook integration: disabling requires account owner to 2FA so will need to figure that out before removing it from this workflow @bmmpxf

Thanks! I'd guess the person who has the 2FA is @jacklaing .

It's not a blocker for this particular PR, but just something we don't need to have anymore.

[bmmpxf]

@jessicadaugherty If you have the ability to merge this, please do whenever you get the chance, as I don't appear to have access (which is fine).

[jessicadaugherty]

So sorry @bmmpxf thought you could do the honors yourself. Done!

[bmmpxf]

Thank you @jessicadaugherty !