Revamp of `data-raw/assemble_bundled_data.R` script

[Kdreval]

The script is cumbersome and hard to manage at the moment. Any update is time consuming since multiple objects are assembled at different places, there is semi-duplication of code, re-assignment of the same variables. etc.
The script should be cleaned up and updated

[Kdreval]

Still some better organization possible but the #122 updates hopefully make it more straightforward. Resolved in #122