ENH: gargle-style authentication

[muschellij2]

Allow for gargle (https://github.com/r-lib/gargle) style of authentication in rgoogleslides::authorize. See https://gargle.r-lib.org/articles/gargle-auth-in-client-package.html for information. I'll try to adapt the code so it will work if I have time.

[hairizuanbinnoorazman]

Seems some of the packages that employed such styles of authentication include https://github.com/tidyverse/googlesheets4 and https://www.tidyverse.org/blog/2019/08/googledrive-1-0-0/

Might be good to take a look at such packages to do a comparison and to understand how it's being done now. Current authentication style in the package was based on rgoogleanalytics (when it was first conceived - it would probably would have been updated by now - haven't exactly checked on it for quite a while)

[hairizuanbinnoorazman]

Attempted to shift to using gargle - unfortunately, this seems like a really huge change. It requires a change on the underlying level. It brings up the question whether such a change is worth it since it would involve changes to function signatures as well for the authorize methods etc