feat: improve requirements file structure

[aht007]

Description

This PR updates the structure of requirements file. With the newer approach, dependencies will only appear in corresponding layer file and not repeated in multiple file. Each requirements file will have just the dependencies needed for the packages listed in the file currently being processed, but at versions compatible with the previous layer of dependencies.

What we hope to gain from this change are the following:

1. Faster make upgrade performance by not having to process as many dependencies for each layer

2. Better ease of reviewing dependency updates, since most dependency versions will only appear in a single requirements file, whereas many currently appear in 3 or more.

Issue: https://2u-internal.atlassian.net/browse/BOM-2483