Refactor dolt_use() to enable 'HEAD' and 'HEAD~2' style commit hash aliases

[n8layman]

This can be done using a query such as:

'select dolt_checkout("main", "HEAD")'

instead of what we currently use:

'use `dbName/hash`'

[noamross]

Should we change the name of the function? USE isn't that intuitive and not really paralleled in the CLI API.