Add Localnet-based automated tests

[fadeev]

• on each PR in the toolkit repo we clone example-contracts
• build and link the toolkit
• cd example-contracts/examples/call && yarn link @zetachain/toolkit
• run localnet.sh

This way we wouldn't have to duplicate any testing logic (the same localnet sh script is used) and will test both if toolkit works and how example will work with the changes introduced in the toolkit.

One thing to consider. When making breaking changes to the toolkit, the automated tests will fail, because they're using main branch of example-contracts. Let's say a toolkit PR introduced a different set of arguments for evm-call, main branch of example contracts will fail, because they'll be using the pre-PR syntax. It is important to handle this scenario, perhaps, by passing a commit hash of a corresponding PR in example-contracts repo.