Stop depending on docs-data branch

[pedro-psb]

The docs-data was introduced so any build of the doc (from dev or CI) could have access to a cached openapi-specs of all components.
But now I realize that relying on that introduces a significant single point of failure.

For example, when we introduce a new component to the documentation, the docs-data branch doesnt not have it's openapi spec yet.
While it is not updated (via the automatic CI), all builds will fail.

Requirements:

• Stop depending on docs-data and remove it
• Improve generating specs from plugin git repositories (e.g, use pulp base-image for sys dependencies)
• Be able to to use caching for the openapi specs (stored on XDG_CACHE_DIR/pulp/pulp-docs/openapi/{cache-key}.json)
• Be able to generate specs from a running instance