Separate out test case generation from deployment

Rather than looping over branches (in included template from `pages`),
generate the test cases here, provide these as an artifact and deploy
in a separate job. This avoids the regeneration of pages that have
not changed.

Use the apertis-test-cases-web as part of a multi-project pipeline to
deploy.

Whilst we are here, utilise an environment variable for the release to
make it easier to migrate this between releases.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>