Extract current Expectations via API

[JoaoGFarias]

Describe the feature request
To have a GET endpoint in MockServer's API that returns in its payload a list of all Expecations currently
existing in a MockServer instance.

What you are trying to do
Currently, MockServer's API allows the user to introduce Expectations to a MockServer instance.

However, a feature that could useful for teams is to allow user to fetch all existing Expecations in a MockServer.

This can be specially useful for those who deal with MockServer programatically, where the set up of MockServer in a particular state can be difficult without the code that makes the setup.

With this, people could share JSON files that can be used to setup other MockServer instances (via the PUT endpoint mentioned above), allowing exploratory testing sessions in a particularly complex Expectation setup, without having to run code that creates this setup programatically.

Describe alternatives you've considered
We could have a button on the UI that downloads a JSON file that represents all Expectations.