Issue 602: Warn about key-uniqueness enforcement to types:Dictionary

[ajnelson-nist]

This Pull Request will resolve all requirements of Issue #602 .

Coordination

• [x] Pull Request is against correct branch
• [x] Pull Request is in, or reverted to, Draft status before Solutions Approval vote has passed
• [x] CI passes in UCO feature branch against develop
• [x] CI passes in UCO current unstable branch (0a6de6f)
• [x] CI passes in CASE current unstable branch tracking UCO's unstable as submodule (0210da1)
• [x] Impact on SHACL validation reviewed for CASE-Corpora
• [x] Impact on SHACL validation remediated for CASE-Corpora (N/A)
• [x] Impact on SHACL validation reviewed for CASE-Examples
• [x] Impact on SHACL validation remediated for CASE-Examples (N/A)
• [x] Impact on SHACL validation reviewed for casework.github.io
• [x] Impact on SHACL validation remediated for casework.github.io (N/A)
• [x] Milestone linked
• [ ] Solutions Approval vote logged on corresponding Issue (once logged, can be taken out of Draft PR status)