feat(nextjs): add optional argument to fetch a new cts when getCtsToken

[calvinbrewer]

getCtsToken previously took no arguments are relied on the Cipherstash session cookie to be set. Now if you optionally provide a user JWT to getCtsToken and the cookie doesn't exist, then a new CTS token will be fetched a returned at run time.

Before:

const ctsToken = getCtsToken()

After (pseudo code):

const { getToken } = auth()
const userJwt = await getToken()

const ctsToken = getCtsToken(userJwt)