skip pending deployments in a queue

[alexanderniebuhr]

• Design doc reviewed with the team
• Project plan reviewed with @EvanBoyle

if multiple commits are pushed to an repository in an on-push scenario an deployment is triggered for every commit. The deployments run sequentially. If all the commits are on the same branch, the latest commit / deployment, will include all the changes of the commits / deployments before it.
I propose to add an configuration flag which enables skipping of pending deployments in a queue except the current running and the last one. We currently merge multiple PRs at a specific time range, and end up with 10s of deployments, restarting our services multiple times (which is uncessary). some note copied over from slack:

• we are currently interested in the push-to-deploy scenario, however I think having it configurable for different combinations of triggers would be great
• cancelled deployments should be still shown in the UI, GitHub Actions has an similar approach (see screenshot)

[EvanBoyle]

We could optionally make this configurable as well. There may be multi-step rollouts that depend on several updates being run in sequence. We did this recently with our MySQL 5.6 EOL upgrade.

[glena]

The feature was implemented and is already available in production. The documentation can be found here https://www.pulumi.com/docs/pulumi-cloud/deployments/reference/#skip-intermediate-deployments