Move LumiSummary offsets header file back into Allen
The header defining the lumi summary counter offsets was moved to LHCb when it was shared with the decoding. As the decoding no longer uses it and it can cause issues if Allen and LHCb MRs aren't performed in parallel, this MR moves it back.
LHCb!3880 (merged) depends on this MR and can be merged immediately afterwards.
Edited by Daniel Charles Craik