API Catalog feature

# Summary
Many organizations use CKAN as a **data portal and catalog**. However, there is an emerging need to catalog data sources from remote **APIs** (e.g. REST, etc.).

It would prove beneficial for CKAN to support some sort of API catalog.

# Background
There are national and EU-wide initiatives to standardize data infrastructure, and CKAN is well positioned. However, CKAN mainly lacks the API cataloging capabilities increasingly needed by governments and industry.

# Idea
An API Catalog would be a top-level feature, on the level of Organizations, Groups, Data Sets, etc.. An API manager could add information about the API, such as the endpoints and documentation in a standard format (such as OpenAPI Specification).

## Extension across CKAN features
Additional features could be built around the APIs, such as comments/feedback, branding, etc. Those features could be related to APIs, data sources, groups, organizations, etc.

*Full disclosure*: I work on an open-source project, called [APInf](https://github.com/apinf/platform), where we have built an API catalogue and community platform.

Start by reviewing the CKAN main repository and Discussions, since this ideas repository is marked deprecated. Compare the proposed top-level API Catalog with existing Organizations, Groups, and Data Sets, and review the OpenAPI requirements described here. Done would require an agreed scope and implementation plan; this issue names no files or tests.

Written by the indexing model from the issue text.