Add clean state example

[itegulov]

Hopefully this is what we are looking for but lmk if you need anything more in-depth

[ailisp]

I suggest to add a short instruction about how to use this contract. In summary, the steps are:

1. Deploy this contract to the account where you want to clean up state
2. Call the contract with known state keys to clean state. If delete all keys doesn't fit gas limit, you may need to do it a few times
3. Once finished clean up state, Deploy the original contract or delete the contract code with near js remove

[itegulov]

Done, PTAL

[ailisp]

Overall the implementation and test is good! Docs need some update to help new developers

[volovyks]

Cool!
From now on we will need to add each example to the examples CI job (check .github/ folder).

[itegulov]

@volovyk-s done!

[itegulov]

@volovyk-s seems like the CI has run out of space. Can we upgrade the instance?

Or I guess alternatively clean up node_modules after we are done with each example

[ailisp]

Looks great!