Payload load data of different modality into cache

**Is your feature request related to a problem? Please describe.**
Follow up on https://github.com/asyml/forte/pull/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 By implementing this feature, we also need to remove old DataPack methods such `set_text` and `set_audio` as it's outdated.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 https://github.com/asyml/forte/issues/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.

**Additional context**