feat: introduce requirements as layers

[efiop]

Drops unused install_requirements that was introduced recently and introduces a new more generic requirements layers. E.g.

requirements = [
    ["foo", "bar"],  # first layer, installed first
    ["baz", "qux"],  # second layer, installed second
    ...
]

For the record: no per-layer cache for now, cached as a whole.

[linear]

INFRA-1449 feat(sdk): install_requires

[chamini2]

Small detail.