Allow a worker to use KMS auth but accept PKI for proxy (#2206)

This essentially worked for non-dev mode before but would create storage
directories that weren't actually used or needed, and it didn't work in
dev mode because it made assumptions about the presence of a worker auth
kms or not. This fixes those behaviors.

internal/cmd/base/servers.go

@@ -126,6 +126,10 @@ type Server struct {
 	DevTargetSessionConnectionLimit  int
 	DevLoopbackHostPluginId          string
 
+	// DevUsePkiForUpstream is a hint that we are in dev mode and have a worker
+	// auth KMS but want to use PKI for upstream connections
+	DevUsePkiForUpstream bool
+
 	EnabledPlugins []EnabledPlugin
 	HostPlugins    map[string]plgpb.HostPluginServiceClient