Create a Swift Package to consume in sentry-cocoa

[philprime]

To be able to consume sentry-conventions as a Swift Package Manager dependency, we need to create a a standard Swift package.

This includes:

• Package.swift in the repository root
• Source code can be in custom nested path
• Tagged commits is enough to define releases

Ideas to brainstorm and discuss:

1. We should consider using strongly-typed enums over static constants, if it has a benefits
2. We need to decide if we build it on-top of external tooling such as SwiftGen or if we want to build custom scripts

References:

• Generated localization strings in Flinky using SwiftGen

[linear-code]

CON-100