Toplevel README doc section for "Getting Started" should mention api endpoint URIs

[truedat101]

In https://github.com/eclipse/hawkbit?tab=readme-ov-file#getting-started (README.md)

it would be helpful to mention the URIs for accessing:

• openapi JSON endpoint: /v3/api-docs
• openapi YAML endpoint: /v3/api-docs.yaml
• swagger_ui endpoint: /swagger-ui/index.html

Some digging around and it looks like in the Docker maps to the above URIs. I realize the API docs are linked in the main docs to the eclipse org site, but this possibly isn't available on easily when developing offline, so it's nice to know how to quickly get to this.

If I've missed this somewhere else in the docs this can be closed.