permission maybe wrong for RocksdbMetadataStore

**Describe the bug**
While RocksdbMetadataStore init , it will create directory from dataPath use Files.createDirectories(dataPath); this path create with too loose that any one can read file in this directory.This may cause everyone can read logs, perhaps strict permission is more safe.

**Expected behavior**
Perhaps right permission for metadata directory is 700.

**Additional context**
I commit this for PULSAR-18 and PR for #15381

Start with RocksdbMetadataStore initialization and the Files.createDirectories(dataPath) call described in the issue. Reproduce the directory creation and inspect the existing discussion around PULSAR-18 and PR #15381. Done means the metadata directory has the intended 700 permissions without breaking initialization.

Written by the indexing model from the issue text.