port `write_dwc()` to use API

[PietrH]

Base on vcr branch and immediately implement cached API responses for tests

• [x] deprecate connection
• [x] split tests: local connection
• [x] split tests: api
• [x] #300
• [x] cache API response
• [x] implement sql helper
• [x] test sql helper
• [x] update NEWS?
• [x] deprecate directory
• [x] reinstate directory
• [x] ignore passing directory to helper functions: add ignore_arguments argument to conduct_parent_to_helpers()
• [x] setup optional writing functionality after conduct_parent_to_helpers()
• [x] make sure write_dwc(api = TRUE) uses RDS/compression
• [x] Check if I can use DBI::dbDisconnect() after all, it seems to work for the other functions, so why not here?

[PietrH]

write_dwc() is the only function that has a deprecated argument other than connection: directory, this argument is passed in the payload and causing an invalid request to openCPU.

This is because the arguments that should not be passed to the API are hardcoded in the conduct_parent_to_helpers() function:

https://github.com/inbo/etn/blob/ee49b2d1194666a790fa554ac3f00176c2a72351/R/utils.R#L354-L362

It might be better if deprecated arguments could be explicitly passed to this function as arguments, the api argument should never be passed to etnservice

[PietrH]

I can use DBI::dbDisconnect() here, and everywhere, because a connection is created for every query, and then closed again after the query.

In etnservice we had a connection leak causing too much resources to be used and the database to run out of connections. However, there might be a performance penalty.

I'm leaving it in for now.