The flux composite bundles together the two individual flux operator
functions, but it fails to provide a `replacements/` to bundle together
their replacements. This results in sites in airshipctl and
treasuremap needing to pull in the function replacementes individually
at the site level, negating the benefit of the composite abstraction.
This adds the replacements kustomization and adjusts test-site to use it.
Change-Id: Ib08e24bdd6ec8222363137bd09ad79dbcd804490
ce5ca13b61