Update docs to reflect removal of cloud and addition of enterprise

[hasheddan]

Description of your changes

Updates documentation to reflect that the cloud group has been brought to top-level as Upbound commands that can interact with hosted or self-hosted installs. Also adds documentation for new up enterprise commands.

Signed-off-by: hasheddan georgedanielmangum@gmail.com

Also removes ineffectual --force flag from up enterprise upgrade.

I have:

• [x] Read and followed Upbound's contribution process.
• [x] Run make reviewable to ensure this PR is ready for review.
• [ ] Added backport release-x.y labels to auto-backport this PR, as appropriate.

How has this code been tested

This is mostly just documentation changes, but I have also tested that up enterprise upgrade still functions properly with --force removed.