ci: Bump containers reusable workflow version to `v0.29.0`

[ppawlowski]

Description

This pull request updates the reusable workflows to the v0.29.0 version. In this particular version, the build_container_image workflow has been refactored. Starting from v0.29.0 workflow builds a single architecture using the platform defined via build_platform input. Additionally, the step responsible for building a multiarchitecture image has been removed, cutting down the time needed, to build the image.

Related Issue(s)

closes https://github.com/FlowFuse/helm/issues/456

Checklist

• [x] 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

Labels

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

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