[FEATURE] Add authorization documentation

[Kern--]

Description

The SOCI snapshotter's authorization setup is not immediately obvious. It doesn't share authorization with the containerd client that normally performs a pull and instead relies on either docker credentials or kubernetes credentials. Both require additional setup when using SOCI with private images.

The only documentation we have is to do sudo docker login in our getting started doc which is not realistic in a production environment. Additionally, since SOCI tries hard not to fail an image pull, if it doesn't have credentials it will fall back to pulling with the client which will likely succeed. This leads to confusion about SOCI's performance being on-par or worse than without because it's doing work and then doing a normal image pull anyway.

Describe the solution you'd like

[ ] A doc outlining the authorization options and their configuration
[ ] Update to debug.md to include looking for authorization errors when the SOCI performs worse than ahead-of-time pulls

Describe any alternative solutions/features you've considered

N/A

Any additional context or information about the feature request

#642 (reply in thread)

[Kern--]

This is done via #1237