feat: add example for docs of migration

[fospring]

Pre-flight checklist

• I have read the Contributing Guidelines on pull requests.
• Commit messages follow the conventional commits spec
• If this is a code change: I have written unit tests.
• If this is a new API or substantial change: the PR has an accompanying issue (closes #0000) and the maintainers have approved on my working plan.

Motivation

for the example of https://docs.near.org/build/smart-contracts/release/upgrade

Test Plan

Related issues/PRs

[ailisp]

Code looks good! have you test the contract? It would be best to have a test included and at least manually tested with CLI. If tested with CLI, also mention the command in doc!

[fospring]

Code looks good! have you test the contract? It would be best to have a test included and at least manually tested with CLI. If tested with CLI, also mention the command in doc!

ok,test file and cli command added, mention command and testfile in this MR

[ailisp]

Looks great!