The action.yml file defines the inputs and outputs for a GitHub Action. This file contains metadata about the action, including the required inputs and outputs, as well as other configurations like the action's description, runs, and environment setup.

Searching the GitHub Marketplace for verified actions published by the cloud provider is the quickest and safest approach. Many cloud providers offer verified GitHub Actions that are maintained and optimized to interact with their services. These actions typically come with the correct configurations and best practices, allowing you to get started quickly without reinventing the wheel.
Note: About GitHub Marketplace for apps
GitHub Marketplace where you can share your apps with everyone.
GitHub Marketplace connects you to developers who want to extend and improve their GitHub workflows. You can list free and paid tools for developers to use in GitHub Marketplace. GitHub Marketplace offers developers two types of tools: GitHub Actions and Apps, and each tool requires different steps for adding it to GitHub Marketplace.
GitHub Actions
Anyone can publish an action in GitHub Marketplace. GitHub verifies some partner organizations and these are shown as verified creators.
Reference:
https://docs.github.com/en/enterprise-cloud@latest/apps/github-marketplace/github-marketplace- overview/about-github-marketplace-for-apps

Managing custom actions
Choosing a location for your action
If you're developing an action for other people to use, we recommend keeping the action in its own repository instead of bundling it with other application code. This allows you to version, track, and release the action just like any other software.
Creating a separate repository for each custom action allows you to manage the versioning independently for each action. This approach provides flexibility, as each action can be updated, tested, and versioned separately, avoiding potential conflicts or dependencies between different actions.
Reference:
https://docs.github.com/en/actions/how-tos/create-and-publish-actions/manage-custom-actions

The repository_dispatch event allows you to trigger a workflow in response to external activity. It is commonly used when you need to trigger a workflow from outside GitHub, such as from another system or service, by sending a request to the GitHub API. This event provides flexibility to integrate with various external systems and trigger workflows in a GitHub repository.

Calling a reusable workflow
You call a reusable workflow by using the uses keyword. Unlike when you are using actions within a workflow, you call reusable workflows directly within a job, and not from within job steps.
jobs.<job_id>.uses
You reference reusable workflow files using one of the following syntaxes:
*-> {owner}/{repo}/.github/workflows/{filename}@{ref} for reusable workflows in public and private repositories.
* ./.github/workflows/{filename} for reusable workflows in the same repository.
Reference:
https://docs.github.com/en/actions/how-tos/reuse-automations/reuse-workflows