OpenAPI generator use case: recurring vs. one-time

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## Suggestion

The current [OpenAPI generator](https://loopback.io/doc/en/lb4/OpenAPI-generator.html) seems like it's meant to be used once, upfront, to scaffold code.

My suggestion is to (also/instead) support the use case where you run the generator regularly as part of your build, and don't even check in the generated files. (this is how I generally prefer to use code generators)

Was this considered in the design of the current generator? Is it possible to achieve something like this with LoopBack today?

## Details

I'm starting a new project, and I expect to gradually evolve the schema over a couple years. Here's how I want it to work when a developer is updating application code to account for changes in the schema:
- pull down the new schema
- run the application build (this runs the code generator, replacing all the generated files)
- application code that references the generated files now has TypeScript errors, showing you where your attention is needed. (follow the squiggles)

Other desirable properties of code generators:
- Generated files have a recognizable, git -ignorable ending (e.g. `.gen.ts`)
- There's a big scary header comment at the top saying "THIS IS A GENERATED FILE, DO NOT EDIT"
- Ideally the generated code is formatted, at generation time, according to the project's prettier config. (for example, see [graphql-code-generator](https://graphql-code-generator.com/docs/integrations/prettier))
- You never need to make a change in a generated file. Instead you make changes in the generator's _input_. (e.g. the OpenAPI schema or in the generator configuration)
- Because the generated file is unversioned and replaced wholesale, you're never asked to resolve a merge conflict between the new template and your project-specific changes.

## Alternatives

- Is Loopback's OpenAPI generator built on top of other libraries or tools that I might be able to use separately?
- Do you know of other node.js web frameworks that might align with this philosophy? I don't need all the features loopback provides, I'm just hoping to make my OpenAPI schema the source of truth for endpoint declarations, input/output types, etc.

Beginne mit der verlinkten OpenAPI generator-Dokumentation und prüfe, wie LoopBack den Generator derzeit ausführt. Vergleiche dieses Verhalten mit dem angeforderten Workflow für wiederkehrende Builds, einschließlich nicht versionierter generierter Dateien, Markierungen für generierte Dateien, Formatierung und TypeScript-Feedback. Als abgeschlossen gilt die Aufgabe, wenn ein abgestimmtes Design und eine unterstützte Möglichkeit zur Verwendung des Generators aus Application-Builds vorliegen.

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