Add E2E testing framework MVP (#1395)

* Add missing words to spellcheck dictionary

* Add `contracts-node.scale` metadata

Has been exported via

	cargo install subxt-cli
	subxt metadata > contracts-node.scale

For `substrate-contracts-node` v0.20.0.

* Run `substrate-contracts-node` in CI

* Invoke `cargo doc` separately for each crate

* Add MVP for E2E testing framework

* Add E2E tests for `contract-transfer` example

* Add ToDo comment for migration to `state_call` RPC

* Update to new `ink` entrance crate

* Add ToDo for `node_log_contains`

* Update to `ink` entrance crate

* Migrate to `state_call` RPC

* Always initialize `env_logger`

* Use latest `subxt` release

* Remove superfluous TODO

* Apply `cargo fmt`

* Adapt test fixtures
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