[app][github] GitHub issue label management

[at15]

This a meta issue for introducing a new app

Currently I am working on a unified set of labels across projects, this requires creating a bunch of labels and pick the right color, which is boring and error prone. In the future, this logic in this app can be used for GitHub bot and assign label based on issue content

• [x] need to introduce global ayi configuration, ~/.ayi.yml or ~/.ayi to store github token
• [x] create the new app, might just name it github because it's a flat package, it won't conflict with https://github.com/google/go-github
• [x] allow read a initial set of labels from a yaml config file, in the future, might use rcl
• [ ] update the labels of an existing project, make a back up before doing so
• [ ] pick the color platte

Ref

• https://github.com/tonglil/labeler saw it from k8s
• https://github.com/flutter/flutter/labels flutter use labels and gh project a lot (170 labels ...)