Auto comment the benchmark CI result to the PR by bot

[loloicci]

Summary

Now, https://github.com/line/lbm-sdk/blob/dynamic_link/.github/workflows/bench.yml benchmarks cosmwasm API for each PRs. But the result can be checked only in the stdout of this workflow. It is better that this result can be checked in the PR page.

Proposal

Modify the workflow into the following:

• When the benchmark ends, a bot comments the result on the PR page.
• Get the base branch's benchmark result, calculate diff and leave it on the comment

---

For Admin Use

• [ ] Not duplicate issue
• [ ] Appropriate labels applied
• [ ] Appropriate contributors tagged
• [ ] Contributor assigned/self-assigned