[Feature] Add Metrics from GitHub's Metrics API to our package

### Is there an existing feature request for this?

- [X] I have searched the existing issues

### Describe the Feature

A fivetran customer submitted a Feature Request for the Metrics API to be added to our Fivetran schema. This actually makes more sense to be part of our dbt package as additional models.

Feature Request by Customer: https://support.fivetran.com/hc/en-us/community/posts/6171852652055-Connector-Improvement-Github-Metrics

GitHub's Metrics API: https://docs.github.com/en/rest/metrics

### Describe alternatives you've considered

Adding the metrics API to the schema but that goes against our product principals as it's denormalized data.

### Are you interested in contributing this feature?

- [ ] Yes.
- [ ] Yes, but I will need assistance and will schedule time during your [office hours](https://calendly.com/fivetran-solutions-team/fivetran-solutions-team-office-hours) for guidance.
- [X] No.

### Anything else?

We should compare what results are returned from the GitHub Metrics API to what we pull from our connector. For example the metrics API has "weekly commits" - can we reverse engineer "weekly commits" by using our commits table?

The goal would be to not need to add anything else to our schema and be able to create these metrics ourselves within a dbt package!

まず GitHub Metrics API のドキュメントを読み、返されるメトリクスと、コネクタがすでに取得しているデータを比較します。既存のテーブルから導出できるメトリクスを特定し、サポート対象のメトリクスをスキーマを変更せずに再現する dbt モデルを定義します。この issue ではファイルやテストは指定されていません。

索引モデルが issue の本文から書いたものです。