Token Refreshing of YouTube doesn't work

[hlxid]

Description

The automatic token refreshing of the YouTube service doesn't work. The service works while the access token is valid. Once it is invalid because it didn't get refreshed and you do anything with the service it will create an error that no refresh token was provided.

As we are at YouTube auth anyway we can also implement saving of the tokens to the config.

How to reproduce

1. Create a youtube service
2. Wait for the access token to invalidade
3. Do any API call

Error Log

UNHANDLED PROMISE REJECTION!
Error: No refresh token is set.
    at OAuth2Client.refreshTokenNoCache (/home/pi/nodecg-io/node_modules/google-auth-library/build/src/auth/oauth2client.js:162:19)
    at OAuth2Client.refreshToken (/home/pi/nodecg-io/node_modules/google-auth-library/build/src/auth/oauth2client.js:143:25)
    at OAuth2Client.getRequestMetadataAsync (/home/pi/nodecg-io/node_modules/google-auth-library/build/src/auth/oauth2client.js:259:28)
    at OAuth2Client.requestAsync (/home/pi/nodecg-io/node_modules/google-auth-library/build/src/auth/oauth2client.js:332:34)
    at OAuth2Client.request (/home/pi/nodecg-io/node_modules/google-auth-library/build/src/auth/oauth2client.js:326:25)
    at createAPIRequestAsync (/home/pi/nodecg-io/node_modules/googleapis-common/build/src/apirequest.js:273:31)
    at Object.createAPIRequest (/home/pi/nodecg-io/node_modules/googleapis-common/build/src/apirequest.js:53:16)
    at Resource$Playlists.list (/home/pi/nodecg-io/node_modules/googleapis/build/src/apis/youtube/v3.js:1815:44)
    at Timeout._onTimeout (/home/pi/nodecg-io/samples/youtube-playlist/extension/index.js:11:49)
    at listOnTimeout (internal/timers.js:554:17)
    at processTimers (internal/timers.js:497:7)

References

Bug report on discord