refactor: exclude indices directory during backup (#6753)

#### What type of PR is this?

/area core
/kind improvement
/milestone 2.20.x

#### What this PR does / why we need it:

备份时排除全文索引目录 indices，防止恢复之后因为索引文件问题无法启动。

#### Which issue(s) this PR fixes:

Fixes #6443

#### Does this PR introduce a user-facing change?

```release-note
备份时排除全文索引目录 indices，防止恢复之后因为索引文件问题无法启动。
```

application/src/main/java/run/halo/app/migration/impl/MigrationServiceImpl.java

@@ -64,6 +64,7 @@ public class MigrationServiceImpl implements MigrationService, InitializingBean
         "backups/**",
         "db/**",
         "logs/**",
+        "indices/**",
         "docker-compose.yaml",
         "docker-compose.yml",
         "mysql/**",