Ci/fix build pipeline for v2

[aljoshare]

Unfortunately, PR #245 seems to have broken the push of docker images for v2 -> https://github.com/glauth/glauth/actions/runs/1907893346. This PR tries to fix it and contains the following changes:

• Copy the working directory instead of the non-existent folder local/app
• Don't change working directory to v2 in Github actions
• Because of the change of the working directory, set the relative path (including v2) to the v2 Dockerfile when running docker build

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

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[Fusion]

Thank you for the pull request.
Note that we are now pushing to Docker using the Makefile target releasedocker and we should remove this Github workflow as it creates confusion.