Add optional telemetry

[krlmlr]

We want to know which query types are triggering a fallback to dplyr. For this, we want to collect the structure of the tables involved (with anonymized column names) and the actual query sent (only the failing part). We will post this anonymized data to an endpoint, using a variant of the following code:

print(httr::content(httr::POST('https://duckplyr-telemetry.duckdblabs.com/', httr::content_type('text/plain'), body=si, encode='raw')))

The response is a handle that allows us to identify the request.

The telemetry will be completely opt-in, users will have to set an option to enable it. The first time a fallback occurs, users will see a prompt that allows them to share, opt-in permanently, or opt-out permanently.