Add type definition on CloudflareWorkerKV for list() about cloudflare-typescript-workers

[dhaynespls]

Yup! Working on it right now.

[sodabrew]

Yep, Cloudflare helpfully provided the type def! Would you be up for opening a PR?

Types
The full signature of the list method (in TypeScript) is:

Namespace.list({prefix?: string, limit?: number, cursor?: string})

All arguments are optional:

• prefix is a string that represents a prefix you can use to filter all keys.
• limit is the maximum number of keys returned. The default is 1000, which is the maximum. It is unlikely that you will want to change this default, but it is included for completeness.
• cursor is a string used for paginating responses. See below for more.

[dhaynespls]

Should be good to go, let me know if I missed anything!