It's desirable (see #6) to be able to enumerate the updates that were
made by automation, in the commit message and perhaps in an event
announcing success.
Doing this is counter-intuitively difficult. A `kyaml.setters2.Set`
filter will keep a count of the times its used. Previously, one `Set`
was used with the `SetAll` flag set, which would replace any marker
that corresponded to an image, in one traversal. But to keep track of
images individually, you need to have a setter for _each_ image (and
its tag, and its name, since those can be used separately). This means
`3 x policies` traversals of each node! The saving grace, possibly, is
that only files with a marker in them are considered.
Since you might want to dice the results in different ways, the result
returned is a nested map of file->object->image.
Signed-off-by: Michael Bridgen <michael@weave.works>
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