repo-file-sync-action Fix: Create Commit tree using GitHub API

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Changes the way that we are creating GitHub trees, because we are hitting some problems on the GitHub side receiving 502 status code with no more information than "Server Error" when creating the tree using the API, and this kind of error is not documented in GitHub but I was able to found some other repositories referencing to this.

This PR changes the way that we create a git tree in GitHub. Now, instead of creating the full tree to commit, we create a new tree with only the changes and references to the git tree of the previous commit in the Create Tree API.

I found the issue https://github.com/BetaHuhn/repo-file-sync-action/issues/246 after getting the same error in some syncs. The code has been tested with my own repositories with this kind of error.

Also, why I changed some imports: I have changed the imports of fs-extra and nunjucks because while running the src/ code locally with node v16.20.2 I was getting an error saying the function fs.existsSync doesn't exist, but it was working just fine if I run the packaged dist version. After looking at the documentation, I changed it to the recommended.

But after making the previous change, I was receiving an error with the nunjuncks which said the function nunjucks.configure did not exist.