🐛轴标题展示问题

### 🐛 Bug description [Please make everyone to understand it]

> Please provide a link by forking these links [G2Plot](https://codesandbox.io/s/g2plot-issue-template-gzfdq?file=/index.ts) or GitHub repo, a minimal reproduction.

* _Required_ **Link to minimal reproduction**:

### 📷 Step to reproduce

### 🏞 Expected result

### 🚑 Any additional [like screenshots]

* **G2Plot Version**:
* **Platform**:
图表的轴标题的位置太受限制了，比如y轴的标题只能在左侧添加吗？x轴标题只能在下方添加吗？我想实现下面这个效果应该怎么办呢？


Start with the linked G2Plot minimal-reproduction template and compare the reported axis-title placement with the attached image. Trace the axis-title configuration and determine whether the requested x- and y-axis positions can be represented; done means the reproduction supports the shown placement or documents the limitation clearly.

Written by the indexing model from the issue text.