Two comments are created instead of one

## Problem
Function [leaveComment](https://github.com/benchmark-action/github-action-benchmark/blob/master/src/write.ts#L242) is called with different commentId, causing 2 comments in PR being created and updated.

Currently, I have 2 PR comments - [one for passed tests](https://github.com/benchmark-action/github-action-benchmark/blob/master/src/write.ts#L269), [another for failed tests (alert triggered)](https://github.com/benchmark-action/github-action-benchmark/blob/master/src/write.ts#L294). I would like to have one PR comment created and updated across all workflow runs within that Pull Request.

## Suggestion

One of these solutions
- allow customising this behaviour with github action option (options like "single_pr_comment" or "custom_comment_id")
- unify `commentId` to be just the value of `benchName` always (when it's alert or not)

If you don't have time to implement this option, are you open to contributions?