Allow for pre-loading OpenAPI

[Dodecahedra]

In our project generating Swagger for large instances can take a long time, causing a long delay for the user (30+ seconds). After upgrading from 1.4.4 to SpringDoc 1.4.6 our existing solution no longer works. We currently have a custom pre-loader that forces OpenAPI to generate swagger by making a HTTP request to SpringDoc when the application starts

Our proposal would be to allow for pre-loading swagger when starting the application, using a method call.

[bnasslahsen]

@Dodecahedra,

Do you have any PR to propose?

[Dodecahedra]

Not yet, I can open one if you are interested.