feat(settings): migrate AppAPI ExApps management to settings

[andrey18106]

Summary

This PR migrates the UI for ExApp management to default Apps management page (settings app). On backend side in settings app there is only addition for initial state for ExApps UI. All ExApp related logic is in separate store that uses backend API part of AppAPI. Also small fix for markdown render.

TODO

• [ ] Requires https://github.com/nextcloud/app_api/pull/417 AppAPI side changes
• [ ] Backport both to stable30

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• [ ] Tests (unit, integration, api and/or acceptance) are included
• [ ] Screenshots before/after for front-end changes
• [ ] Documentation (manuals or wiki) has been updated or is not required
• [ ] Backports requested where applicable (ex: critical bugfixes)