fix: credential secrets: avoid race condition when prompting user (#2410)

[g-linville]

for #2410

There is a race condition that occurs only when deploying an acorn to the SaaS that defines a credential secret. The user will be prompted to enter credentials multiple times because the app keeps changing upstream. If we wait for a little bit (until all containers are marked as Defined), the race condition doesn't occur, and the user is only prompted once.

I also tested this with Acornfiles that only define this secret and a nested acorn, as well as an Acornfile that defines just the secret and nothing else, and it still works just fine.

Checklist

• The title of this PR would make a good line in Acorn's Release Note's Changelog
• The title of this PR ends with a link to the main issue being address in parentheses, like: This is a title (#1216). Here's an example
• All relevant issues are referenced in the PR description. NOTE: don't use GitHub keywords that auto-close issues
• Commits follow contributing guidance
• Automated tests added to cover the changes. If tests couldn't be added, an explanation is provided in the Verification and Testing section
• Changes to user-facing functionality, API, CLI, and upgrade impacts are clearly called out in PR description
• PR has at least two approvals before merging (or a reasonable exception, like it's just a docs change)

[njhale]

late to the party, but lgtm anyway

[njhale]

nano-nit:

Suggested change

	err := login.Secrets(d.ctx, d.client, app)
	if err != nil {
	go d.Errorf(err.Error())
	} else {
	d.lastLogin = app.Generation
	}
	if err := login.Secrets(d.ctx, d.client, app); err != nil {
	go d.Errorf(err.Error())
	} else {
	d.lastLogin = app.Generation
	}