Plan for migration to googleAuthR 2.0 - splitting out into smaller packages

[MarkEdmondson1234]

I'd like to split out the functions and refactor now I know more R. The auth features are now covered by gargle so I'd like to instead depend on more packages in the downstream dependencies rather than keep updating this one.

Eventually googleAuthR 2.0.0 will just be wrappers for the smaller packages, then it can be retired gracefully e.g. no version 3.0.0. Probably be a few more years at least before this happens.

The features I'd like to break out are:

• Google auth gargle - done
• shiny auth - in progress maybe in gargle or another package https://github.com/r-lib/gargle/pull/157#issuecomment-728260285
• discovery API package builder https://github.com/MarkEdmondson1234/googleAuthR/blob/master/R/discovery.R
• Service email APIs (IAM functions https://github.com/MarkEdmondson1234/googleAuthR/blob/master/R/service_creation.R )
• Package setup wizards https://github.com/MarkEdmondson1234/googleAuthR/blob/master/R/setup_wizard.R
• Auto-paging, caching and batching for Google APIs (make something that generalises to all APIs?)

[MarkEdmondson1234]

The biggest blockers at the moment for migrating downstream packages are shiny auth and the paging/caching/batching features so it looks like splitting them out first will be a good first priority.