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/core/consensus/consensus.go b/metropolis/node/core/consensus/consensus.go
index f6addd8..f00a7a9 100644
--- a/metropolis/node/core/consensus/consensus.go
+++ b/metropolis/node/core/consensus/consensus.go
@@ -33,12 +33,12 @@
 //   | node-foo            |
 //   |---------------------|
 //   | .--------------------.
-//   | | etcd               |<---etcd/TLS--.   (node.ConsensusPort)
+//   | | etcd               |<---etcd/TLS--.   (allocs.PortConsensus)
 //   | '--------------------'              |
 //   |     ^ Domain Socket |               |
 //   |     | etcd/plain    |               |
 //   | .--------------------.              |
-//   | | curator            |<---gRPC/TLS----. (node.CuratorServicePort)
+//   | | curator            |<---gRPC/TLS----. (allocs.PortCuratorService)
 //   | '--------------------'              | |
 //   |     ^ Domain Socket |               | |
 //   |     | gRPC/plain    |               | |