Bug: UPSTREAM_REPO: unbound variable

[JaimieWi]

Addition to re-install the install-azure-tre-oss.sh script was required to pick up changes to the container when running in GitHub Actions.

# Re-run the install-azure-tre-oss.sh script
echo "Re-running install-azure-tre-oss.sh..."
bash /tmp/install-azure-tre-oss.sh "${UPSTREAM_REPO}" "${UPSTREAM_REPO_VERSION}" "${AZURETRE_HOME}" "${GITHUB_TOKEN}"

The above was added, but causes a failure when running the container locally.

[9521 ms] Start: Run in container: /bin/sh -c ./.devcontainer/scripts/post-create.sh
Re-running install-azure-tre-oss.sh...
./.devcontainer/scripts/post-create.sh: line 19: UPSTREAM_REPO: unbound variable
[10135 ms] postCreateCommand from devcontainer.json failed with exit code 1. Skipping any further user-provided commands.
Done. Press any key to close the terminal.

The post-create script fails because it tries to use UPSTREAM_REPO, UPSTREAM_REPO_VERSION, and GITHUB_TOKEN as environment variables, but these are only defined as Docker build arguments and don't persist to the running container.

Fix: Update .devcontainer/scripts/post-create.sh to read from the files created during build instead:
UPSTREAM_REPO=$(cat "${AZURETRE_HOME}/repository.txt")
UPSTREAM_REPO_VERSION=$(cat "${AZURETRE_HOME}/version.txt")