Changed the issue cross-reference row in the header table to use a designated proposal label.

Author: tedepstein

proposals/2019-01-01-Proposal-Template.md

@@ -10,7 +10,7 @@
 |Review Manager | TBD |
 |Status |Proposal, Draft, Promoted, or Abandoned|
 |Implementations |[Click Here](https://github.com/OAI/OpenAPI-Specification/tree/main/proposals/{YYYY-MM-DD-Short-Name}/implementations.md)|
-|Issues |[{issueid}](https://github.com/OAI/OpenAPI-Specification/issues/{IssueId})|
+|Cross-Reference |_Assign a unique label for this proposal, keeping the "Proposal-" prefix, and edit the label filter in the links._<br/><br/>Label: Proposal-Xref-Label<br/>[Related Issues](https://github.com/OAI/OpenAPI-Specification/issues?q=is%3Aissue+label%3AProposal-Xref-Label)<br/>[Related Pull Requests](https://github.com/OAI/OpenAPI-Specification/issues?q=is%3Apr+label%3AProposal-Xref-Label)|
 |Previous Revisions |[{revid}](https://github.com/OAI/OpenAPI-Specification/pull/{revid}) |
 
 ## Change Log