Add Dependabot Automation

[patinthehat]

Overview

This PR adds dependabot automation for this repository.

Description

This PR adds a dependabot configuration file that enables weekly update checks for all github actions used within workflows in the project (if it does not exist).

Additionally, it includes a workflow that automatically merges dependabot PRs for minor and patch version updates (major version bumps must be manually merged to avoid breaking changes, with one exception - see below).

Finally, Github Actions that have a major version update AND a compatibility score of >=90% are automatically merged as way to reduce the manual work of merging PRs that are of no risk of breaking changes. ONLY Github Actions that have a major version update are considered for automatic merging. Other dependencies are excluded.

Using these features will help keep all workflows up to date with a minimal amount of manual intervention necessary.

Notes

This functionality has already been added to the Spatie laravel package skeleton repository.

[freekmurze]

Thanks!