Add helper functions for OAUTH2 authentication (#109)

[jason-p-pickering]

• Add token to d2Session object

• Add OAUTH login function

• Update NAMESPACE

• Documentation and cleanup

• Update rocker verse R version

• Update lock

• Minor

• Fix R6 import

• Linting

• Add lintr to suggests

[jason-p-pickering]

@JordanBalesBAO or @sam-bao ...any objections to me proceeding to merge the OAUTH stuff into master?

[sam-bao]

@JordanBalesBAO @jason-p-pickering no specific blockers from me. I would probably increment the version to 0.6.0 since this is a major new feature. Jordan is closer to this now and should provide the full review.

I did just add a ticket to update datapackr's lock file to the version of datimutils with the OAUTH work (https://jira.pepfar.net/browse/DP-782). It seems good practice to keep the datapackr and app dependencies roughly synchronized.

[jason-p-pickering]

Thanks @sam-bao . I bumped the version now. @JordanBalesBAO has previously provided his technical review here.

@JordanBalesBAO if you are OK with everything, please approve here as well, and I can proceed with updating the app code.

[JordanBalesBAO]

I agree adding the token to the overall structure of the R6 object is a good idea.