Patch/schematic api

[anngvu]

One of of the two endpoints we wrap (manifest_generate) needs to be updated with schematic changes announced this morning, so if you are using this then please reinstall package after this is merged. Close #127.

Test:

library(nfportalutils)
syn_login(Sys.getenv("SYNAPSE_AUTH_TOKEN"))
`manifest_generate("ImagingAssayTemplate", "syn38849300", output_format = "google_sheet")`
# Link downloaded as "ImagingAssayTemplate.csv"
manifest_validate(data_type = "ImagingAssayTemplate", file_name = "ImagingAssayTemplate.csv")

[allaway]

Works great when testing!