Implement client-side function to recombine partial-exit blobs (recombineExitBlobs)

[LukeHackett12]

Create a client-side function, recombineExitBlobs, to stitch together a list of valid partial-exit blobs into a full exit message. Note: The same approach is intended for both solutions.

https://github.com/ObolNetwork/charon/blob/491a0e1f9cf958325fc1f3abdbd550dd09453a32/app/obolapi/exit.go#L165

and the tbls.ThresholdAggregate(rawSignatures) is an implementation of this
https://eth2book.info/capella/part2/building_blocks/signatures/#aggregation
nothing fancy