Add support for configuring `lenient: true` in `.swiftlint.yml`

[F1248]

New Issue Checklist

• [x] I've Updated SwiftLint to the latest version.
• [X] I've searched for existing GitHub issues.

Feature or Enhancement Proposal

Since I can't pass command line arguments like --lenient when using SwiftLint through the SwiftLintBuildToolPlugin, writing lenient: true in .swiftlint.yml would be the perfect way to configure this, just as it was implemented with strict in #5226.