`CREATE DATABASE` location

#451 implemented support for `CREATE DATABASE` queries.
It includes two tests for the query.

`Statement::CreateDatabase` has two additional fields: `location` and `managed_location`. The syntax for these is not detailed; neither in the PR, nor anywhere else I can find.

1. Perhaps this could be detailed in the docs
2. Perhaps tests could be added for these fields
3. What is the syntax for these fields?

先檢視 PR #451 和現有的兩個 CREATE DATABASE 測試，接著檢查 Statement::CreateDatabase，包括其中的 location 和 managed_location 欄位。確立兩個欄位的語法並加以文件化，新增涵蓋該語法的測試，讓行為清楚明確。

由索引模型根據 Issue 內容生成。