WIP: Resolve "VAT Import Project Creation"

Closes #133 (closed) This MR deletes the vat_import.py script from the pipeline and instead brings it in from the new VAT Import project within the ironbank-tools group. This allows for the VAT team to own their import script, add tests, and have a custom pipeline.

• Remove requirements.txt from pipeline and retrieve from VAT Import project
• Change URLs for vat_import.py and requirements.txt to be variables