We have a number of trace attributes that we use across all of our OCI
Distribution-based functionality, so this centralizes their definitions
in package traceattrs.
This intentionally ignores a few additional attribute names that are used
only in the code that interacts with Docker-style credential helpers,
because all of those are used only in a single function and so adding
indirection for those doesn't have enough benefit to offset the cost of
additional indirection.
Signed-off-by: Martin Atkins <mart@degeneration.co.uk>
93d095c67e