Document lake output format and add/update ls docs

[philrz]

What's Changing

• The -f lake output format is documented
• Docs are added for zed ls
• Command help docs are updated for zed ls

Why

When creating the "output formats" table in #5170, I spotted lake as one of the output formats available via -f in the zq -h help text. I wasn't previously familiar with it, but I asked around to get consensus on whether it should be documented or hidden. @mccanne ultimately was slightly in favor of documenting it, so that's the main thing I set out to do here.

Details

Once I got started, I realized I wanted to hyperlink to docs about the zed ls command and only then noticed we didn't have a section in the zed command doc about it, so I went to add one based on the current zed ls -h command help text. However, that help text seemed somewhat out-of-sync with its current behavior, so I corrected that as well.

Closes #5169