docs: restructure references

[IronCore864]

Some structural changes to the reference docs.

Changes:

• Remove duplicated commands from subdirectories in the reference, and move the examples in them to cli-commands.
• Remove directories "notices", "changes-and-tasks", "pebble-in-containers", change them into a single page under "reference".
• Update broken links because of the above structural changes.
• Set terminal width to a fixed length so that the actual terminal width where the script is running won't affect the help command output width.

[AnneCYH]

Hi @IronCore864 , some minor comments.
Am just focusing on the intended scope of this PR.

[AnneCYH]

Hey @IronCore864 , some general feedback.

The cmd pages should link back to the parent reference page, where available.
E.g. notices CLI pages should link back to the Notices reference doc.

But it can be an enhancement.

[IronCore864]

Hey @IronCore864 , some general feedback.

The cmd pages should link back to the parent reference page, where available. E.g. notices CLI pages should link back to the Notices reference doc.

But it can be an enhancement.

Thanks for the advice, I just added them in this PR since it's only adding a line and it's related to the moved content anyway.

[benhoyt]

Looks good to me, thanks. I also tweaked the pebble run and pebble warnings help descriptions to be wrapped to 80 columns manually -- it's a bit unfortunate these use a fixed wrapping and the args help uses an automatic wrapping, but oh well. This is good enough for now.