add changelog bot to dbt-common

### Housekeeping

- [X] I am a maintainer of dbt-common

### Short description

Add the changelog bot ([dbt-core example](https://github.com/dbt-labs/dbt-core/blob/main/.github/workflows/bot-changelog.yml)) so that changelogs are automatically added for dependabot.

### Acceptance criteria

Changelogs get automatically added for dependabot changes

### Suggested Tests

None

### Impact to Other Teams

None

### Will backports be required?

no

### Context

Make sure all the necessary secrets exist. Look at the root action to determine what secrets are needed.