m/node/allocs: split new package off m/node

The metropolis/node package contains various unrelated things. One of
these things are node-wide allocations of identifiers.
These are moved here to the new metropolis/node/allocs package.
Additionally, the constants are renamed to move the type of identifier
in front.

Change-Id: Ibc841ca64d4450a7054463e6d2d44753a118e07a
Reviewed-on: https://review.monogon.dev/c/monogon/+/4566
Reviewed-by: Tim Windelschmidt <tim@monogon.tech>
Tested-by: Jenkins CI
diff --git a/metropolis/node/allocs/doc.go b/metropolis/node/allocs/doc.go
new file mode 100644
index 0000000..dcc6960
--- /dev/null
+++ b/metropolis/node/allocs/doc.go
@@ -0,0 +1,6 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+// Package allocs contains allocations of various types of identifiers used in a
+// node. By tracking these centrally, we can avoid collisions.
+package allocs