feat: add finally hook

[mdonnalley]

Add finally hook that will run at the end of every command execution - regardless of success or failure.

Usage

// src/hooks/finally.ts
import {Hook} from '@oclif/core'

const hook: Hook.Finally = async function (opts) {
  this.log(`I finally finished running ${opts.id} with args: ${opts.argv.join(' ')}`)
}

export default hook

Issues

Closes #1275
Closes #1263
Closes #1264
@W-17482601@