Change title and hierarchy

[dai-chen]

Issue #, if available:

Description of changes: Change troubleshoot and PartiQL section title. Group SQL sections into same hierarchy as https://github.com/opendistro-for-elasticsearch/sql/blob/master/docs/user/index.rst.

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[dai-chen]

I was trying to organize SQL sections into same hierarchy as docs in sql repo: https://github.com/opendistro-for-elasticsearch/sql/blob/master/docs/user/index.rst. However I found that each level seems required to be a folder with a index.md. But our intermediate level actually does not have any content. Are you aware of any workaround? Thanks.

[dai-chen]

Here is the hierarchy we want:

 1. Workbench
 2. CLI
 3. ODBC driver
 4. JDBC driver
 ---- Same as index.rst ----
 5. Data Query Language
   5.1 Basic Queries
   5.2 Complex Queries
   5.3 Metadata Queries
   5.4 SQL Functions
 6. Beyond SQL
   6.1 JSON Support
   6.2 Full-text Search
 7. Data Manipulation Language
   7.1 Delete Statement
 8. Interfaces
   8.1 Endpoints
   8.2 Protocol
 9. Administration
   9.1 Monitoring
   9.2 Plugin Settings
 10. Troubleshooting
 --------------------