Well, think about a goldfish bowl for a moment. It is completely open to the eyes of the outside world because the bowl is transparent. This expression is therefore used as a metaphor to describe a situation where someone has little or no privacy, or where the state of affairs of someone's life are known by many people. The meaning is entirely unrelated to the idiom 'in a nutshell.' I have also heard it used to describe a situation where someone feels trapped because of this lack of privacy. It ties in quite nicely because obviously a fish is unable to escape from a goldfish bowl.

Paul has given an excellent answer. I would only give an example here: the Duchess of Cambridge. She lives in the public eye. She has very little privacy in her life. Hers is life lived in a goldfish bowl.

I have never heard of this one but I would imagine yes. A similar idiom though would be, life in a nutshell- which means, that's the basic concept, or the short story of something. For example: "...and then I passed my language course, and that was my year, in a nutshell." I'm not sure if the two are exactly related.