Payload load data of different modality into cache

[hepengfe]

Is your feature request related to a problem? Please describe.
Follow up on #828, I complete a draft that Payload can holds loading method and load path(assigned in reader), and they can be used together to achieve lazy loading in processor (rather than reader). However, load data into payload cache is not implemented yet. By implementing this feature, we also need to remove old DataPack methods such set_text and set_audio as it's outdated. DataPack should supports multiple Payloads with different Modality.

It's also part of #810

Describe the solution you'd like

• remove Datapack.set_text and Datapack.set_audio.
• add cache assignment in Payload.load

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

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