[continuous deployment] Automatically deploy a staging test environment on swh_next_version MR

The goal is to validate the next version images and behavior before applying the MR in all the staging environments

changed milestone to %Design and test a Continuous Deployment infrastructure [Roadmap - Tooling and infrastructure]

assigned to @vsellier

mentioned in commit swh/infra/ci-cd/k8s-clusters-conf@ff136b95

mentioned in commit swh/infra/ci-cd/k8s-clusters-conf@84def59f

mentioned in commit swh/infra/ci-cd/swh-charts@71750820

The automatic deployment is working quite well, except a couple of points:

• as expected staging needs more resources
• on undeploy, the storage is stopped before the loader generating a lot of resolving errors (storage service not found), we should find a way to progressively undeploy the environment
• the environment should be deployed if some migrations are needed (storage, webapp, scheduler (for later), indexer storage (for later), swh-search)

mentioned in commit swh/infra/puppet/puppet-swh-site@9740f5a8

mentioned in merge request swh/infra/puppet/puppet-swh-site!632 (merged)

mentioned in commit swh/infra/ci-cd/swh-charts@cf983bf3

mentioned in commit swh/infra/ci-cd/swh-charts@fdec04b4

mentioned in commit swh/infra/ci-cd/swh-charts@e38179a7

mentioned in commit swh/infra/ci-cd/swh-charts@5107b848

mentioned in commit swh/infra/ci-cd/swh-charts@f9e8e0a4

mentioned in commit swh/infra/ci-cd/swh-charts@a824e99c

mentioned in commit swh/infra/ci-cd/swh-charts@223ba873

mentioned in commit swh/infra/ci-cd/swh-charts@b83acfd3

mentioned in commit swh/infra/ci-cd/swh-charts@1f79b836

mentioned in commit swh/infra/ci-cd/swh-charts@b84fe0b4