build: separate each build into its own job so can be released separately

[rchincha]

Is your feature request related to a problem? Please describe.
Currently, we build everything every time we cut a release. Only build when the specific config changes for a particular image.
So separate builds into static.yaml, base.yaml, ... etc

But also keep an option to trigger a full build if need be - assuming zothub.io contents are lost, etc.

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