Finalize option interface

[krlmlr]

Support options in addition to (or instead of) env vars.

[maelle]

Actually seeing this, maybe telemetry should not be one file per option as in my PR but instead there could be a duckplyr configuration file? https://blog.r-hub.io/2020/03/12/user-preferences/#using-a-config-file

[maelle]

This way, all options would be in one place. Maybe it could somehow be created by default, to show the default options.

[maelle]

The setting of options could happen via functions, or manually.

There could be several locations for the configuration file like for an .Rprofile (user-level vs project-level).

Having it all in one file means it's easier for users to get an overview but probably also for us to document all options somewhere central?

[krlmlr]

Yeah, the user interface vs. the actual storage of the options are two separate questions. I'll think about it and work with what's in the PRs.

[krlmlr]

Descoping, the env var interface is good enough.