improve REDCapR's approach for catching & throwing errors --while providing useful context to the user

[wibeasley]

A few years ago I changed how errors were thrown because I was worried about it revealing tokens or other secrets. But I went too far and too much is concealed. We'll switch to rlang's approach:

• https://rlang.r-lib.org/reference/abort.html
• https://rlang.r-lib.org/reference/topic-error-chaining.html

It may make sense to wait until moving to httr2 (#430), since hhtr2 will handle errors differently than httr:

HTTP errors are automatically converted into R errors. Use req_error() to override the defaults (which turn all 4xx and 5xx responses into errors) or to add additional details to the error message.