[FEATURE] Include event labels in `redcap_events` tibbles

[ezraporter]

Feature Request Description

Events in longitudinal redcaps can have custom labels in addition to identifiers:

The redcap_events columns of the supertibble should include these labels.

Proposed Solution

The event labels are accessible with the Export Events API method but REDCapR doesn't currently have a wrapper for this. We can make an issue and supply the code. Once that's running in REDCapR it will be easy to add this field to redcap_events by modifying link_arms().

Checklist

• [x] The issue is atomic
• [x] The issue description is documented
• [x] The issue title describes the problem succinctly
• [x] Developers are assigned to the issue
• [x] Labels are assigned to the issue