add changelog bot to dbt-common

[emmyoop]

Housekeeping

• I am a maintainer of dbt-common

Short description

Add the changelog bot (dbt-core example) 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.