Feature: allow `include` to allowlist certain packages

[Spence1115]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the feature has not already been requested

🚀 Feature Proposal

Rather than just an exclude list to prevent certain packages from automerging, could there be an include option, to allow only those packages to automerge?

Motivation

Right now if we want to limit automerging to only certain packages we trust, we would need to update the exclude list every time a developer adds a new package, which is likely to be forgotten. Allowing us to only mark certain packages as allowed via an include list would solve this problem, and feels in keeping with the rest of the action.

Example

steps:
  - uses: fastify/github-action-merge-dependabot@v3
    with:
      include: 'vitest,eslint'