Document best practices when dealing with multiple channels

[anmazzotti]

Once ready to publish all the different channels, we need to provide user feedback with the best practices on how to deal with them.

Most notably:

• Document the sync behavior and the relation between ManagedOSChannel and ManagedOSVersions
• Document how to delete a channel and what are the consequences of doing so (ManagedOSVersions ownership will delete them in cascade, what if they are in use?)
• Document the .json schema we use for custom channels. (Highlight the ManagedOSVersion name collision problem when making your own custom channels)
• Document the best practice of naming the channel using the base OS name+flavor
• Disclose the list of available channels (all tags/flavors)
• Document the meaning of flavors. How is base different than baremetal? When should I use what. What about the other flavors?

[anmazzotti]

Best practice for naming a channel should be {BaseOS}-{BaseOSVersion}-{Flavor}.

For example:

name: sle-micro-5.5
uri: registry.opensuse.org/isv/rancher/elemental/dev/containers/rancher/elemental-channel/sle-micro:5.5

name: sle-micro-5.5-kvm
uri: registry.opensuse.org/isv/rancher/elemental/dev/containers/rancher/elemental-channel/sle-micro:5.5-kvm

name: sle-micro-5.5-rt
uri: registry.opensuse.org/isv/rancher/elemental/dev/containers/rancher/elemental-channel/sle-micro:5.5-rt

In this way it should be possible to decouple the "elemental build version" (ex. v2.0.2-4.2.20) from the base os version (5.5), while still referencing the latter.

It will look something like this on the UI extension: