Add ability to align FAB group

**Is your feature request related to a problem? Please describe.**
For my use case, I need the Fab group to be align to the bottom left of the screen instead of the bottom right. 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 an "align" property to Fab.Group to align the group to the left or center instead of just the right.

**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.

Fab.Group のエントリーポイントから始め、現在の右下への配置がどのように定義されているかを確認します。left、center、right を対象とする align オプションを追加し、グループが要求された各位置にレンダリングされることを確認します。

索引モデルが issue の本文から書いたものです。