--startup-project is missing

In given options and the example ``--startup-project `` option is missing. So command failing.

[This solution](https://stackoverflow.com/questions/56686093/unable-to-create-an-object-of-type-dbcontext/69207083#69207083) got nearly 100k view for simple required option

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#### Document Details

⚠ *Do not edit this section. It is required for learn.microsoft.com ➟ GitHub issue linking.*

* ID: b545eeff-6c33-3cc0-09ce-a3ad342d7438
* Version Independent ID: 34bc1bac-7338-d8ab-390d-8c5e88a48c10
* Content: [Using a Separate Migrations Project - EF Core](https://learn.microsoft.com/en-us/ef/core/managing-schemas/migrations/projects?tabs=dotnet-core-cli)
* Content Source: [entity-framework/core/managing-schemas/migrations/projects.md](https://github.com/dotnet/EntityFramework.Docs/blob/main/entity-framework/core/managing-schemas/migrations/projects.md)
* Product: **entity-framework**
* Technology: **entity-framework-core**
* GitHub Login: @bricelam
* Microsoft Alias: **avickers**