Add GitHub Actions workflow for on-demand releases

[pablomendezroyo]

This pull request introduces a new GitHub Actions workflow for manual releases, enabling on-demand publishing of the project using a custom setup. The workflow is triggered manually and automates the process of checking out the code, setting up Node.js, logging into the GitHub Container Registry, and publishing using the DappNode SDK.

Release workflow automation:

• Added .github/workflows/release-on-demanda.yml to define a manual workflow (workflow_dispatch) for triggering releases.
• Configured steps to check out code, set up Node.js (20.x), log in to GitHub Container Registry, and publish using @dappnode/dappnodesdk with custom providers and timeout.<!-- For DAppNode core members, once the Pull Request is created, do not forget to:

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