Allow data frame to be passed to `add_resource()`

[peterdesmet]

movepub::add_resource() currently only supports files to be added. That is a bit annoying for tests, for example here where we have to revert to using frictionless:

movepub/tests/testthat/test-write_dwc.R

Lines 26 to 30 in db4c6f6

	# Create package, use frictionless::add_resource() to add df rather than csv
	x_missing_ref_cols <-
	create_package() |>
	frictionless::add_resource("reference-data", iris) |>
	frictionless::add_resource("gps", gps)

Maybe we should allow data frames as well (cf. frictionless::add_resource()).