chore (changelog): add pki workers (#2218)

CHANGELOG.md

@@ -5,7 +5,9 @@ Canonical reference for changes, improvements, and bugfixes for Boundary.
 ## Next
 
 ### New and Improved
-
+* PKI Workers: This release introduces a new worker type `PKI`, which
+  authenticate to Boundary using a new certificate-based method, allowing for
+  worker deployment without using a shared KMS.
 * Credentials: This release introduces a new credential store type `static`,
   which simply takes in a user-supplied credential and stores it (encrypted)
   directly in Boundary. Currently, the `static` credential store can hold