This PS adds decoding features to ReplacementTransformer to decode
the source objectRef when source is of `kind: Secret` and has `data`
field. It also encodes the value in the target fieldRefs before
replacement if the target is `kind: Secret` and has `data` fields.
Throws an error if the target fieldRefs have both `data` and `stringData`
for replacement.
Change-Id: I1d918058409b3511faa9a99512d25574027bda86