Implement migration for v2.1.2

This migration writes the current version number to the data directory.
The remaining migrations depend on another open PR and will follow soon.

application/src/main/java/bisq/application/migration/Migrator.java

@@ -1,11 +1,11 @@
 package bisq.application.migration;
 
 import bisq.application.migration.migrations.Migration;
+import bisq.application.migration.migrations.MigrationsForV2_1_2;
 import bisq.common.platform.Version;
 import lombok.extern.slf4j.Slf4j;
 
 import java.nio.file.Path;
-import java.util.Collections;
 import java.util.List;
 
 @Slf4j
@@ -17,7 +17,7 @@ public class Migrator {
     public Migrator(Version appVersion, Path dataDir) {
         this.appVersion = appVersion;
         this.dataDir = dataDir;
-        this.allMigrations = Collections.emptyList();
+        this.allMigrations = List.of(new MigrationsForV2_1_2());
     }
 
     public void migrate() {

application/src/main/java/bisq/application/migration/migrations/MigrationFailedException.java

@@ -0,0 +1,7 @@
+package bisq.application.migration.migrations;
+
+public class MigrationFailedException extends RuntimeException {
+    public MigrationFailedException(Throwable cause) {
+        super(cause);
+    }
+}

application/src/main/java/bisq/application/migration/migrations/MigrationsForV2_1_2.java

@@ -0,0 +1,26 @@
+package bisq.application.migration.migrations;
+
+import bisq.common.application.ApplicationVersion;
+import bisq.common.platform.Version;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+public class MigrationsForV2_1_2 implements Migration {
+
+    @Override
+    public void run(Path dataDir) {
+        try {
+            Path versionFilePath = dataDir.resolve("version");
+            Files.writeString(versionFilePath, ApplicationVersion.getVersion().toString());
+        } catch (IOException e) {
+            throw new MigrationFailedException(e);
+        }
+    }
+
+    @Override
+    public Version getVersion() {
+        return new Version("2.1.2");
+    }
+}

application/src/test/java/bisq/application/migration/migrations/MigrationsForV2_1_2Tests.java

@@ -0,0 +1,28 @@
+package bisq.application.migration.migrations;
+
+import bisq.common.application.ApplicationVersion;
+import bisq.common.platform.Version;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class MigrationsForV2_1_2Tests {
+    private final MigrationsForV2_1_2 migrationsForV212 = new MigrationsForV2_1_2();
+
+    @Test
+    void migrationTest(@TempDir Path dataDir) throws IOException {
+        Version version = migrationsForV212.getVersion();
+        Version expectedVersion = new Version("2.1.2");
+        assertThat(version).isEqualTo(expectedVersion);
+
+        migrationsForV212.run(dataDir);
+        String readVersion = Files.readString(dataDir.resolve("version"));
+        assertThat(readVersion)
+                .isEqualTo(ApplicationVersion.getVersion().toString());
+    }
+}