dynamic host volumes: send register to client for fingerprint (#24802)

When we register a volume without a plugin, we need to send a client RPC so that
the node fingerprint can be updated. The registered volume also needs to be
written to client state so that we can restore the fingerprint after a restart.

Co-authored-by: Daniel Bennett <dbennett@hashicorp.com>

demo/hostvolume/no-plugin.volume.hcl

@@ -0,0 +1,15 @@
+# Copyright (c) HashiCorp, Inc.
+# SPDX-License-Identifier: BUSL-1.1
+
+name = "no-plugin"
+type = "host"
+
+# this volume spec can be used with 'volume register' after filling in the
+# host_path and node_id values below
+host_path = "TODO" # absolute path of the volume that was created out-of-band
+node_id   = "TODO" # ID of the node where the volume was created
+
+capability {
+  access_mode     = "single-node-writer"
+  attachment_mode = "file-system"
+}