Setup SwiftLint in the project and on CI

[iangmaia]

Description

This PR sets up SwiftLint as a SPM plugin and runs it on CI using the command run-swiftlint.

The main changes:

• Adding the .swiftlint.yml file with the rules currently being checked and defining the SwiftLint version to use
• Usage of the run-swiftlint command from a8c-ci-toolkit-buildkite-plugin in a new Buildkite step.
• Adding SwiftLint as a SPM dependency and plugin
• Fixing the currently found violations in the codebase

Testing Details

Make sure CI is 🟢

---

• I have considered if this change warrants release notes and have added them to the appropriate section in the CHANGELOG.md if necessary.

[dangermattic]

	1 Warning
⚠️	Package.swift was changed without updating its corresponding Package.resolved. Please resolve the Swift packages in Xcode.

Generated by 🚫 Danger

[mokagio]

Verified the SwiftLint output in CI. Thanks @iangmaia