feat: Run Device Agent in container as unpriviledged user

[ppawlowski]

Description

This pull request changes the way how the device-agent runs inside a container. Instead of using a root user, a custom flowfuse one is created during the container build process.

Additionally, it:

• adds a workflow that ensures the container build process is validated against every PR that introduces changes to Docker-related files
• runs Static Application Security Test scan against the built container and pushes results to the GitHub Advanced Security
• Adjusts the node package build pipeline to skip execution if Docker-related files are modified

Related Issue(s)

Closes #562

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production
• Link to Changelog Entry PR, or note why one is not needed.

Labels

• Includes a DB migration? -> add the area:migration label

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[hardillb]

Need to think about this, mainly how it will impact things with mounted volumes as any files written will previously have been owned by root.

Will have to test

[hardillb]

My problem with this is it is potentially a breaking change, so we should merge and apply it the same time we change the default NodeJS version (to 20) at the next major release (4.0.0?).

I'm pretty sure this will break users that are extending the flowfuse/device-agent container (e.g. "windows") as the active user will change from root to a user that can not install apk packages or create new directories.

There is a workaround for the existing container which is to pass -u 1000:1000 to set the uid and gid to 1000 so as not to run as root.

Need to think about this some more

[ppawlowski]

NodeJS v20 has been in maintenance for a long time, and EOL is scheduled for April/May this year. IMO if we are thinking about a breaking change release, we should aim for at least NodeJS v22 (v24 preferably) to avoid having another breaking change release in the middle of 2026.