Rename module and SDK import paths for Threshold

Fork of hashicorp/boundary-plugin-aws (MPL-2.0). Module path and Boundary SDK
imports now point at repo.anhonesthost.net/CyberCoveLLC. Adds NOTICE and an
About this fork section to the README.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

NOTICE

@@ -0,0 +1,9 @@
+This repository is a community fork of hashicorp/boundary-plugin-aws
+(https://github.com/hashicorp/boundary-plugin-aws), maintained for Threshold.
+
+The original work is licensed under the Mozilla Public License 2.0 (see LICENSE).
+Original copyright IBM Corp. / HashiCorp, Inc. is retained in all source file
+headers and in LICENSE. Modifications are limited to the Go module path and the
+import paths of the Boundary SDK/API packages.
+
+This fork is not affiliated with, endorsed by, or supported by HashiCorp or IBM.