[FEATURE] Update Spark Connector formatting

[jeremyprime]

Is your feature request related to a problem? Please describe.

The formatting/code style throughout the Spark Connector is not consistent, and does not always follow a best practice or standard. This can make reading the code more difficult, and also introduces unnecessary changes when different developers are working on the code and creating pull requests.

Describe the solution you'd like

Come up with a formatting convention that works across IDEs (Visual Studio Code, IntelliJ, etc) and provide instructions in CONTRIBUTING.md on how to apply the formatting. And also apply those formatting rules to the existing codebase in a single PR.

Additional context

I think scalafmt works for both VS Code and IntelliJ. Another option is to use Metals (which is integrated with VS Code, not sure about its support in IntelliJ).