prefix search

[rsteube]

Is your feature request related to a problem? Please describe.

Crates.io currently only provides fulltext search which is not very useful for shell completion.

Describe the solution you'd like

Provide a way to search crate names by prefix (e.g. ^json) on crates.io and using the cargo cli.

Describe alternatives you've considered

Accessing the crates.io-index repo using the github contents api seems to work fine so far.

Additional context