[feature-request] support registry-mirrors

[zhuangqh]

Why you need it?

we may pull images from some private image registry.

How it could be?

UX

launch pouchd with --registry-mirrors. registry-mirrors is a string slice. pouch will attempt to use these mirrors in order of the config order.

It is unnecessary to specific the net prototype(http://, https://) in the mirrors configuration. Pouch use https by default.

For http registry, just add them into insecure-registries parameters.

Detail

Pouch will first try the mirrors in the registry-mirrors list, and then the default-registry one.
Only if the domain field in the image reference equals to the default-registry, pouch will add the missing namespace which configured from default-namespace.

Other related information