Add ability to modify the border width of the ActivityIndicator

**Is your feature request related to a problem? Please describe.**
For my use case, I need a large ActivityIndicator but with a thin border width. I am currently using patch-package to hack it, but it would be great to have this added to react-native-paper.

**Describe the solution you'd like**
Add a "borderWidth" property to ActivityIndicator to allow modifying it independent of size (fall back to setting it based on size if not provided).

**Describe alternatives you've considered**
Using patch-package, but it requires changing the patch every time I need to upgrade the package to a new version.

**Additional context**
N/A

I would be happy to work on a PR for this if it's ok to introduce something like this.

首先定位 ActivityIndicator 组件、它的公共 props 以及现有测试。在保留省略该选项时当前基于尺寸的行为的同时，添加所请求的 borderWidth 选项，然后确认组件测试覆盖这两种路径。

由索引模型根据 Issue 内容生成。