`add_age_cat()` breaks should behave with a +1 increment

[gnoblet]

Issue: To be able to have the following thresholds: 0-17, 18-59, 120+, the current breaks must be written not intuitively as follows:

 add_age_cat("resp_age", breaks = c(-1, 17, 59, 120))

Proposed change:

add_age_cat("resp_age", breaks = c(0, 18, 60, 121))

[gnoblet]

@lanawwas assigning it to you since you worked on it. Feel free to disagree and close the issue.

[lanawwas]

We move this to the next release, v2024.1.2