PoC: comments with example of behavior on Observable

[giollord]

Added comments for 6 functions with examples of behavior, similar to how they do it on ReactiveX website.
Also added class to sandbox/ConsoleApp1 that allow to generate more examples.

Not sure if this is a good way to make comments though:

• 🟢 it's informative and could be useful for people like me who are not very familiar with reactive programming
• 🔴 giant comments sometimes being troublesome when they pop up on half of screen.
• 🔴 comments have to be stored in separate xml file
• 🟢 but then can reuse them on other functions

Here is how it looks in VS 2022 on Windows:

Screenshots

P.S.: This PR is more of a proof of concept. Unfortunately, can not guarantee that I will add much more docs even if it gets approved, but I will try to add at least some. Also descriptions and some example data were taken from ReactiveX website.