Fix stream/process name for egamma datasets.

[jomatthi]

This PR renames the 2024 EGamma datasets to be consistent with the 22/23 EGamma datasets.

[riga]

The 22/23 campaigns that I just checked all name it "data_e_*". Which ones were you referring to?

[jomatthi]

I'm referring to the run3_2022/3_pre/postEE/BPix_nano_v12 campaigns, so datasets like this in 2022 postEE:

cpn.add_dataset(
    name="data_egamma_e",
    id=14783260,
    is_data=True,
    processes=[procs.data_egamma],
    keys=[
        "/EGamma/Run2022E-22Sep2023-v1/NANOAOD",  # noqa
    ],
    n_files=188,
    n_events=148654795,
    aux={
        "era": "E",
    },
)

I do see however, that in the nano_uhh_v14 campaigns the other convention is used, so there seems to be some kind of inconsistency.