XDR for upgradeable config entries (#75)

* Generalize configuration-related XDR.

The changes here are summarized in proposed updated to CAP-47 (stellar/stellar-protocol#1291).

- Use unique keys to identify settings
- Only distribute a hash for config upgrades in `StellarValue`
- Add SCP messages for exchanging config upgrade sets

* Remove unused ConfigSetting

---------

Co-authored-by: Dmytro Kozhevin <dmytro@stellar.org>

Stellar-ledger-entries.x

@@ -505,33 +505,15 @@ struct ContractCodeEntry {
     opaque code<SCVAL_LIMIT>;
 };
 
-enum ConfigSettingType
-{
-    CONFIG_SETTING_TYPE_UINT32 = 0
-};
-
-union ConfigSetting switch (ConfigSettingType type)
-{
-case CONFIG_SETTING_TYPE_UINT32:
-    uint32 uint32Val;
-};
-
 enum ConfigSettingID
 {
-    CONFIG_SETTING_CONTRACT_MAX_SIZE = 0
+    CONFIG_SETTING_CONTRACT_MAX_SIZE_BYTES = 0
 };
 
-struct ConfigSettingEntry
+union ConfigSettingEntry switch (ConfigSettingID configSettingID)
 {
-    union switch (int v)
-    {
-    case 0:
-        void;
-    }
-    ext;
-
-    ConfigSettingID configSettingID;
-    ConfigSetting setting;
+case CONFIG_SETTING_CONTRACT_MAX_SIZE_BYTES:
+    uint32 contractMaxSizeBytes;
 };
 
 struct LedgerEntryExtensionV1

Stellar-ledger.x

@@ -130,6 +130,11 @@ enum LedgerUpgradeType
     LEDGER_UPGRADE_CONFIG = 6
 };
 
+struct ConfigUpgradeSetKey {
+    Hash contractID;
+    Hash contentHash;
+};
+
 union LedgerUpgrade switch (LedgerUpgradeType type)
 {
 case LEDGER_UPGRADE_VERSION:
@@ -143,11 +148,11 @@ case LEDGER_UPGRADE_BASE_RESERVE:
 case LEDGER_UPGRADE_FLAGS:
     uint32 newFlags; // update flags
 case LEDGER_UPGRADE_CONFIG:
-    struct
-    {
-        ConfigSettingID id; // id to update
-        ConfigSetting setting; // new value
-    } configSetting;
+    ConfigUpgradeSetKey newConfig;
+};
+
+struct ConfigUpgradeSet {
+    ConfigSettingEntry updatedEntry<>;
 };
 
 /* Entries used to define the bucket list */