Add CLI documentation generator

[patrickbrophy]

This PR addresses issue #2472. This PR allows for documentation to be automatically generated using the go generate command. A minor implementation note, I had to put the generation code in the cmd package because of how Go handles accessing exported variable inside the main package.

[h2zh]

The approach to auto-generating the CLI docs is really clever. Having said that, I think what's implemented in this PR doesn't totally reflect the requirements in the ticket created by @aowen-uwmad. My understanding was that the goal is to have the docs live on the documentation website directly. The current implementation seems to require users to run a manual command to generate and view them. Maybe it is just an intermediate PR?

[CannonLock]

@patrickbrophy These errors aren't tied to anything I can help with. My guess from looking through things is that when Haoming set this up he held an assumption of run order so things didn't break. I see some placeholder magic in the generate folder.

Maybe add this to the generate directory with the other scripts?

[aowen-uwmad]

@patrickbrophy , I know there are some "hidden" commands that dev team doesn't necessarily want users to know about..
Does your auto-generation take those into account (and not generate those pages)?

[patrickbrophy]

Yes the generator takes that into account. A command is "hidden" when the Command.Hidden field is set to true. Below is a screenshot showing that the object delete command is hidden:

[patrickbrophy]

I have updated the layout to be less nested and a lowercase like how our commands are written in the terminal.

[aowen-uwmad]

The screenshot of the updated navigation bar looks good to me.

[aowen-uwmad]

I did a local preview and explored the commands reference pages; I think it looks good.
I can't speak to the Go or CI/CD pieces, though, so someone else should review that to approve this.

[aowen-uwmad]

This PR is blocked by #1765. Will need to be refactored to address the changes in there.