option to identify all possible overlapping intervals

[chacalle]

Describe changes

To help with overlapping intervals where it may not be clear what is truly the less granular interval.

Like: 0-11, 10-15, 15-20 as specified in #66.

We can visually inspect and know 0-11 is the messed up age group likely, but before this PR only 10-15 was flagged as overlapping. Now if identify_all_possible=TRUE is specified, both 0-11 and 10-15 are flagged for manual inspection.

Checklist

Packages Repositories

• Have you read the contributing guidelines for ihmeuw-demographics R packages?
• Have you successfully run devtools::check() locally?
• Have you updated or added function (and vignette if applicable) documentation? Did you update the 'man' and 'NAMESPACE' files with devtools::document()?
• Have you added in tests for the changes included in the PR?
• Do the changes follow the ihmeuw-demographics code style?
• Do the changes need to be immediately included in a new build of docker-base or docker-internal? If so follow directions in those repositories to rebuild and redeploy the images.
• Do the changes require updates to other repositories which use this package? If yes, make the necessary updates in those repos, and consider integration tests for those repositories.
• If this is a private package did you use Jenkins to rebuild the internal pkgdown site?

[chacalle]

The error message on 151 is only triggered if overlapping_dt_severity != "none". We want the error message to show all possible overlapping intervals.

But if the error is skipped then line 155 tries to drop the least granular overlapping interval.