Commands that install/fetch/pin multiple things should be more robust

[mikrostew]

NOTE: this issue predates this project's rename to Volta.

(from #383 (comment))

fetch, pin, and install accept multiple package arguments, like:

notion fetch node [email protected] [email protected]

The current behavior is to fail fast, so in the above example an error fetching node would abort the whole command. We could be more robust and try to handle all of the specified packages, collecting any errors and reporting at the end.

[benblank]

While it doesn't constrain us to do the same, it's worth noting that both npm and Yarn follow the fail-fast path.