Add set_code_hash function and example

[willser]

Add ink_env::set_code_hash and create two examples in examples/upgradeable-contracts/set-code-hash.

Resolves #1185 .

[willser]

Hello team,I checked the CI log and got thoese information.It's that something wrong in this PR?

$ git clone --verbose --depth 1 --branch ${UPSTREAM_BRANCH} ${UPSTREAM_REPO}
Cloning into 'ink'...
warning: Could not find remote branch will/add-seal_set_code_hash-function-and-example to clone.
fatal: Remote branch will/add-seal_set_code_hash-function-and-example not found in upstream origin

UPSTREAM_BRANCH_REDIS_KEY=will-add-seal_set_code_hash-function-and-example
$ echo "UPSTREAM_REPO=${UPSTREAM_REPO}" | tee -a parent-vars.env
UPSTREAM_REPO=https://github.com/paritytech/ink.git
$ echo "UPSTREAM_REPO_NAME=${UPSTREAM_REPO_NAME}" | tee -a parent-vars.env

[cmichi]

Thanks so much for implementing this @willser !