docs,testing(native-federation-runtime): adds mvp of testing with vitest and playwright to native-federation-runtime

[aramirezj]

Context

Since the packages lacks testing and documentation, this PR aims to start providing the package of native federation with some testing tool and comments to increase maintainability.

Detail

1. Adds dependencies for Vitest, playwright and msw
2. Adds unit testing
3. Adds integration testing for the features of init federation and load remote modules with browser mode
4. Renames some functions in init-federation and load-remote for more readability
5. Adds comments explaining steps in complicated logic

Note: The file get-shared technically is not used, so it could be erased, for now it's still there waiting for more info