Added `POST /repository/archive/rebuild` endpoint to allow local archive to be rebuilt.

When "archiveVersion" is set to 2 in settings, this should allow the archive size to reduce by over 90%. Some nodes might want to maintain an older/larger version, for the purposes of development/debugging, so this is currently opt-in.

src/main/java/org/qortal/api/resource/AdminResource.java

@@ -45,6 +45,7 @@ import org.qortal.block.BlockChain;
 import org.qortal.controller.Controller;
 import org.qortal.controller.Synchronizer;
 import org.qortal.controller.Synchronizer.SynchronizationResult;
+import org.qortal.controller.repository.BlockArchiveRebuilder;
 import org.qortal.data.account.MintingAccountData;
 import org.qortal.data.account.RewardShareData;
 import org.qortal.network.Network;
@@ -734,6 +735,52 @@ public class AdminResource {
 		}
 	}
 
+	@POST
+	@Path("/repository/archive/rebuild")
+	@Operation(
+			summary = "Rebuild archive.",
+			description = "Rebuilds archive files, using the serialization version specified via the archiveVersion setting.",
+			responses = {
+					@ApiResponse(
+							description = "\"true\"",
+							content = @Content(mediaType = MediaType.TEXT_PLAIN, schema = @Schema(type = "string"))
+					)
+			}
+	)
+	@ApiErrors({ApiError.REPOSITORY_ISSUE})
+	@SecurityRequirement(name = "apiKey")
+	public String rebuildArchive(@HeaderParam(Security.API_KEY_HEADER) String apiKey) {
+		Security.checkApiCallAllowed(request);
+
+		try {
+			// We don't actually need to lock the blockchain here, but we'll do it anyway so that
+			// the node can focus on rebuilding rather than synchronizing / minting.
+			ReentrantLock blockchainLock = Controller.getInstance().getBlockchainLock();
+
+			blockchainLock.lockInterruptibly();
+
+			try {
+				int archiveVersion = Settings.getInstance().getArchiveVersion();
+
+				BlockArchiveRebuilder blockArchiveRebuilder = new BlockArchiveRebuilder(archiveVersion);
+				blockArchiveRebuilder.start();
+
+				return "true";
+
+			} catch (IOException e) {
+				throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.INVALID_CRITERIA, e);
+
+			} finally {
+				blockchainLock.unlock();
+			}
+		} catch (InterruptedException e) {
+			// We couldn't lock blockchain to perform rebuild
+			return "false";
+		} catch (DataException e) {
+			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.REPOSITORY_ISSUE, e);
+		}
+	}
+
 	@DELETE
 	@Path("/repository")
 	@Operation(