[Feature request] Allow specification of `DefaultRootObject` when creating/updating cloudfront distribution

[iamogbz]

Specific use-case is deploying multiple versions of the app based on the the current git branch, as highlighted by the docs.

You can also specify a path: app.example.com/something. This can be useful to deploy multiple versions of an app in the same s3 bucket. For example one could deploy a feature branch of the SPA like this:

While it is possible to remove the branch name from app.example.com/<branch>, it would be helpful to allow configuring the default root object served when no branch path is given.

Example: Deploying and having the default release branch be main;

• app.example.com -> main/index.html (default)
• app.example.com/main -> main/index.html
• app.example.com/next -> next/index.html
• app.example.com/new-feature -> new-feature/index.html etc.

Open to putting up a PR for the changes needed