Create a Dagster asset that fetches npm downloads

[Jabolol]

What is it?

The dlt connector is already implemented on #2435. Next step would be to get the list of all npm packages we want to index (maybe from ossd?), and wire it together as follows:

oso/warehouse/oso_dagster/assets/npm.py

Lines 102 to 125 in 50e0279

	```python
	# NPM was launched on January 12, 2010
	NPM_EPOCH = "2010-01-12T00:00:00Z"
	@dlt_factory(
	key_prefix="npm",
	partitions_def=WeeklyPartitionsDefinition(
	start_date=NPM_EPOCH.split("T", maxsplit=1)[0],
	end_offset=1,
	),
	)
	def downloads(
	context: AssetExecutionContext,
	):
	yield get_all_downloads(
	context,
	package_names=[
	"@angular/core",
	"react",
	"vue",
	# ...
	],
	)
	```