Make getPluginByName be plugin-aware

[antgamdia]

Extracted from #4764

Summary

getPluginByName is a hardcoded list of plugin objects for getting the object with the version set. Ideally, it should fetch it from the actually configured plugins.

Background and rationale

The UI may want to query the currently enabled working to conditionally enable some options. For instance, filtering by plugin or creating a repository just if the plugin is enabled.

Description

The getPluginByName function should call the plugin API to show all the configured plugins in the API server.

Acceptance criteria

• There is a proper client in the UI for querying the Plugins API
• This client is used by the getPluginByName to return the proper plugin version according to the actually configured plugins

Additional context

The first part of the issue is also required by #3889.