Integrate with OpenAPI editor

Description

OpenAPI aka. Swagger is a widely used API description format. The idea is to:

• render an API directly with swagger-ui within file view
• provide a link to open an api spec directly within a swagger-editor
• further options could be to store changed API from editor back to GitLab

The integration could be similar to plantuml.

Proposal

We would like to contribute this. /cc @siemens

Links / references

• https://www.openapis.org/
• https://swagger.io/swagger-ui/
• https://swagger.io/swagger-editor/

Overview

• What is it? Smooth integration for api development.
• Why should someone use this feature? APIs are widely used.
• What is the underlying (business) problem? faster development cycles without extra tools for APIs
• How do you use this feature? Browser and edit API's

Use cases

Api development with OpenAPI is adopted within many areas.

Feature checklist

Make sure these are completed before closing the issue, with a link to the relevant commit.

• Feature assurance
• Documentation
• Added to features.yml