`argocd-wait` step

[jessesuen]

Proposed Feature

argocd-update only waits until a sync operation completes. However, in applications that have no PostSync hooks or sync waves, this will return immediately, as the sync is essentially a kubectl apply of all manifests.

We need something equivalent to the CLI's:

argocd app wait my-app

NOTE: Kargo already has a wait for health functionality. This occurs as part of an "implicit verification" process to ensure an app is healthy before running analysis. However, this process may be happening too late for some use cases.

Motivation

Users often prefer that the app sync and wait happen as part of a promotion, instead of verification. Some use cases:

1. In an app that contains multiple argocd-updates for different microservices (e.g. backend + frontend) as in the "grouped services" pattern, the backend may need to reach health before the frontend is updated

2. Post update steps, like notifications, could be sent only after ensuring apps are healthy after the update.

[jessesuen]

A gross workaround is to add a PostSync hook resource to the Application. The resource could even be an empty configmap. This changes the Argo CD sync operation to wait until the PostSync phase completes, ensuring that after the argocd-update step is complete, the Application is in a Healthy state.

[eddiewebb]

Issue was linked to Harvestr Discovery: add argocd-wait step

[bmbferreira]

If you're facing issues with sync waves that get into SyncError state and nothing fails on kargo, then I think the issue might be related with what is described on #5166 and with the fix I'm trying to do here