Allow disabling publication of a package from cli when automated publishing is enabled

[sigurdm]

That would make it easier to avoid publication mistakes.

[isoos]

Couple of notes on the backend side:

• I think the related flag should not be part of PkgOptions, since we don't want to expose it publicly.
• The related flag could be part of the existing AutomatedPublishing data structure, but we've discussed that it could be toggled independently. We may even rename the AutomatedPublishing field to PublishingSettings, or just leave the name as-is in this case.
• Or, we could introduce a ManualPublishing class with a now-single bool flag, or it could be a top-level Package.isManualPublishingDisabled field. In either case we'll need to have new HTTP admin endpoint(s) that update (and get) the field value.

On the package admin page it would make sense to create a new top-level entry after the "Automated publishing" section like the following:

[sigurdm]

I think reusing AutomatedPublishing (or renaming it) are good options.

Are we exposing PkgOptions?

[isoos]

I think reusing AutomatedPublishing (or renaming it) are good options.

I'll use it first, we can rename later.

Are we exposing PkgOptions?

Yes: https://pub.dev/api/packages/retry/options