Change type of group id from ParaID to CoreIndex

[axaysagathiya]

Issue summary

Before elastic scaling, only a single group of validators was assigned to a parachain, so we assigned paraID to GroupID.
However, in elastic scaling, multiple groups of validators(core) will be assigned to a parachain. So now we have to change the type of GroupID from paraID to the CoreIndex, which is unique for assigned groups.

• Change the type of groupID from paraID to CoreIndex and check all the methods to see if any changes are needed.
  • Structs containing groupID: Summary, tableContext, attestedCandidate, candidateData.
• change assignment *parachaintypes.ParaID field to assignedCore *parachaintypes.CoreIndex in perRelayParentState which represents the core index assigned to the local validator at this relay parent. also figure out if we really need this a pointer type.

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