Move npm org

[knolleary]

Description

This updates the Device Agent to the new @flowfuse/device-agent npm package and flowfuse/device-agent dockerhub image.

As part of this migration it also:

• Updates the readme to cover the new locations
• Updates the default data directory to /opt/flowfuse-device/ - however it will use /top/flowforge-device if it exists and nothing else has been specified
• Updates the workflow to cross-publish to the existing npm package and container images. This required a dedicated Dockerfile to ensure the proper config directory still exists for the 'legacy' container.
• Adds a startup log message if found to be installed using the old npm package name

The full set of workflow changes are untested - we cannot test it without doing a full release. So please give the workflow changes a particularly close review.

Before we do the first release once merged, we need to update some repo-level secrets:

• NPM_PUBLISH_TOKEN_FLOWFORGE - the token for publishing to old npm org
• NPM_PUBLISH_TOKEN - the token for publishing to the new org
• DOCKER_HUB_PASSWORD_FLOWFORGE - the password for the old dockerhub account
• DOCKER_HUB_PASSWORD - the password for the new dockerhub account

[knolleary]

@hardillb asking you for a review here - in particular, the workflow steps to cross publish.

[hardillb]

Looking