add encoding key to DecReport raw bank

follow changes in LHCb!3528 (merged) to add an explicit encoding key into the DecReports raw bank (and increase its version number).

NOTE: requires LHCb!3528 (merged) in order to have a decoder which can decode this version of the rawbank -- and LHCb!3528 (merged) also requires Moore!1529 (merged) which in turn uses functionality from this MR -- so this MR must be applied in conjunction with LHCb!3528 (merged) and Moore!1529 (merged)