Review help/usage for cli commands

[amritghimire]

let's also make a ticket to review help / usage for all these commands. we have a lot of inconsistencies and bugs here:

• E.g. Commands for managing datasers (let's add a spell checker on pre-commit)

• should be printing usage:

(.venv) ?2 Projects/dvcx % datachain datasets
Error: Unexpected command None

• probably hide things like --pdb, --debug-sql
• review help messages for all commands

Originally posted by @shcheklein in #768 (comment)

[shcheklein]

Only the first iteration is done.

[shcheklein]

@amritghimire reviewed the doc a bit, PTAL and let's do the second quick iteration (apply some things across all commands if it's applicable) and let's renew the document again. Thanks a lot!