Setting the image creation timestamp in the image metadata to a
constant date can cause problems with self-hosted container
registries, that need to e.g. prune old images. This timestamp is
also useful for debugging.
However, it is almost never useful to set the filesystem timestamp to
a constant value. Doing so not only causes the image to possibly no
longer be reproducible, but also removes any possibility of
deduplicating layers with other images, causing unnecessary storage
space usage.
Therefore, this commit introduces "mtime", a new parameter to
streamLayeredImage, which allows specifying the filesystem timestamps
separately from "created". For backwards compatibility, "mtime"
defaults to the value of "created".
847b4732e4