fix(typescript): accept `{ auth: () => }` constructor option

Instead of `{ auth: { auth: () =>  } }`

fix(typescript): two-factor authentication is on2fa() not on2Fa() (oc…

…tokit#1222)

fix(typescript): update typings with new options for constructor

refactor: `github.` -> `octokit.`

feat: userAgent, previews and request options

Deprecates agent, timeout and headers options

build(package): lock file

feat: two-factor authentication

test: un-skip add-labels-to-issue scenario

fix: do not load the same plugin again

feat(typescript): complete `.endpoint` types