OR-5247 Subject

[crazymanish]

Context

• Close ticket: [w17(23april-29april)] Subject: Read books about subject #10

In this PR

• Read the book about the Subject
• https://developer.apple.com/documentation/combine/subject
• https://paigeshin1991.medium.com/swift-combine-currentvaluesubject-the-most-useful-subject-of-all-times-56e197d9bab7

Demo

• Subject is a publisher that exposes a method for outside callers to publish elements.
• A subject is a publisher that you can use to ”inject” values into a stream, by calling its send(_:) method. This can be useful for adapting existing imperative code to the Combine model.