rofl-scheduler: Read offer access policy from on-chain metadata

Move the per-offer allowed_creators and allowed_artifacts access policy
out of the scheduler's local node config and into on-chain offer
metadata, so a provider can change it with a transaction instead of
editing the node config and restarting the machine.

The scheduler now reads these well-known offer metadata keys each round:

  - net.oasis.scheduler.offer.allowed_creators: comma-separated creator
    addresses; empty or absent means all creators are allowed.
  - net.oasis.scheduler.offer.allowed_artifacts.<kind>: comma-separated
    allowed artifact hashes per kind; an absent kind allows all.
  - net.oasis.scheduler.offer.private: marks an offer private so it can
    be hidden from normal offer listings. Read but not acted on by the
    scheduler.

The global allowed_creators and allowed_artifacts fields are removed from
the local config (no fallback); RawLocalConfig now ignores unknown fields
so existing configs still load. Matching metadata-key constants are added
to the Go client SDK for use by the CLI.

Author: anzoman

client-sdk/go/modules/roflmarket/types.go

@@ -124,6 +124,25 @@ type Offer struct {
 	Metadata map[string]string `json:"metadata"`
 }
 
+// Well-known offer metadata keys recognized by the ROFL scheduler.
+const (
+	// MetadataKeyOffer is the offer metadata key holding the offer identifier (the value used by
+	// the scheduler's local config to select which offers it serves).
+	MetadataKeyOffer = "net.oasis.scheduler.offer"
+	// MetadataKeyOfferAllowedCreators is the offer metadata key holding a comma-separated list of
+	// allowed instance creator addresses. When unset or empty, all creators are allowed.
+	MetadataKeyOfferAllowedCreators = "net.oasis.scheduler.offer.allowed_creators"
+	// MetadataKeyOfferAllowedArtifactsPrefix is the prefix of the offer metadata keys holding the
+	// allowed artifact hashes. The artifact kind is the suffix following the prefix (e.g.
+	// "net.oasis.scheduler.offer.allowed_artifacts.firmware") and the value is a comma-separated
+	// list of allowed SHA256 hashes. If no key exists for a kind, all artifacts of that kind are
+	// allowed.
+	MetadataKeyOfferAllowedArtifactsPrefix = "net.oasis.scheduler.offer.allowed_artifacts."
+	// MetadataKeyOfferPrivate is the offer metadata key marking an offer as private. Private
+	// offers are hidden from normal offer listings unless explicitly requested.
+	MetadataKeyOfferPrivate = "net.oasis.scheduler.offer.private"
+)
+
 // Term is the reservation term.
 type Term uint8