add documentation for buckets and resizing a volume

[zalsader]

I don't have access to gitbook, so here's a PR.

[height[bot]]

Previously linked tasks:

• T-9664 Update docs for CLI buckets (relink task)

Link Height tasks by mentioning a task ID in the pull request title or commit messages, or description and comments with the keyword link (e.g. "Link T-123").

💡Tip: You can also use "Close T-X" to automatically close a task when the pull request is merged.