Feature/e2e tests

[boyswan]

Initial e2e testing crate idea

• In order for e2e tests to work in a cargo workspace project (and separate crate), we need to patch ink and ink_e2e with the latest master ink which contains fixes for these issues. Expecting these to be in the 4.0.2 ink release, so we should be able to remove the patch as soon as it's available.

• Currently I'm importing and using the equippable contract for all e2e tests. Perhaps we should have a single "mother" contract in the testing crate which provides a complete implementation of all rmrk functionality, instead of testing examples (which could change). I think there's still a few questions around how this might work.

• Helper directory to avoid duplicating testing logic with a call/query naming convention. These are currently bound to the single imported equippable contract as described above - making this generic is a bit more complex and will require some more thought.

[Maar-io]

The PR #57 introduces integration test in CI and it also have e2e job that needs to be un-commented. Best if you rebase once it is merged.