Support app sync --dry-run --local when automatic sync policy is enabled

[chancez]

Summary

Currently you will get an error if you try to do a local sync with a sync policy of automatic, even if --dry-run is specified:

argocd app sync my-app --dry-run --local
FATA[0000] Cannot use local sync when Automatic Sync Policy is enabled

Dry run should not affect the cluster state, so it shouldn't matter what the sync policy is, so this should be allowed.

Motivation

I'd like to use this to produce the output YAML that ArgoCD would produce so that I can use it with kubectl diff during CI before we merge the changes, so that we can have a preview of the changes before they're applied (similar to terraform plan).

Proposal

ArgoCD should support --local when --dry-run is specified, even if the application has an automatic sync policy configured.

Generally speaking, I think argocd app diff --local works similar to what I would want, but I'd also like to have the capability to do this using kubectl.

[pacoguzman]

@chancez did you find a way to use kubectl diff on pull requests as a way to validate review them?

Thanks in advance

[MeNsaaH]

Same here. wondering how to display diffs to validate PRs. @pacoguzman . Can't seem to get argod app diff --local working. Seems all repo must be local even remote charts