[cli] add kv subcommand

[miguelrk]

The CLI is missing certain utilities to make it easier to manage the KV database across environments (development and production). Some useful utilities include: dump, migrate, mock, reset, restore, seed, upload (from e.g. JSON files), etc.

This issue should replace the db: tasks under e.g. templates/crm/tasks/. The subcommands should ask to specify filepaths to JSON files of KVMutations. As a convention, we use *.entries.json filenames. These files should have be in the form of [Deno.KvMutation](https://deno.land/api?s=Deno.KvMutation&unstable=)[] or { type: "set"; value: unknown; expireIn?: number; }[] for now. Other formats e.g. CSV can be added laterr.