ug: offline-update: Enable App fetching instead of preloading

[mike-sul]

The recent changes to ci-scripts and fioctl allows offline update enabling without turning on the preloading/assembling.

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[doanac]

Docs for 6805a3b are browsable at: https://ci.foundries.io/projects/fio-docs/builds/2638/docs/artifacts/html/index.html

[mike-sul]

The provided mechanism will work only for the fioctl version with this change foundriesio/fioctl#379.

I am not sure if we should mention a specific version of fioctl to make it working. I suppose we just align the docs and fioctl releases (target lmp v94).

[mike-sul]

@vanmaegima @caiotpereira Please, let me know if this change makes sense to you?

This change won't impact existing customers that already turned on the preloading/assemble run to enable offline update (required in order to download apps into an offline bundle). The logic in the fioctl command is smart enough to figure out where to pull apps from.

The goal is to guide new customers to use the new factory configuration parameter containers:offline:enable:true if they would like to include apps into an offline update bundle.

Also, the existing customers that use just offline update and do not need the image assembling/preloading can switch to this way. It will reduce a CI build duration for them because the assemble run is turned off in this case.

[vanmaegima]

Thanks @mike-sul , this makes sense

[mike-sul]

@vanmaegima @caiotpereira This has been deployed to the prod, so the doc update can be merged now.

[kprosise]

LGTM, proceeding with merging