Add new Vue app and entry points for standalone VSA settings page

What does this MR do and why?

As part of the migration of the create/edit form from the modal within the Value Stream Analytics to a standalone settings page, this MR:

• Introduces the VSASettings app behind a new vsa_standalone_settings_page feature flag and entry points to the edit and new views at the group level (project level will be implemented in #442675)
• Provides the necessary data attributes from the backend
• Imports the existing Vuex store from the VSA app
• Ports over the value_stream_form component, modifies it to suit the new settings app's needs and adds a new value_stream_form_content_header component that will be needed once rest of the value_stream_form_content component is ported over.

This is the first of two merge requests to resolve #381002 (closed).

Task	Status
Create new Vue app and entry points at group level for standalone VSA settings page	⬅
Migrate value_stream_form_content to VSASettings app and link to settings page from the Value Stream Analytics application behind a feature flag.	🚧

MR acceptance checklist

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Please make sure that you're on the GitLab Ultimate plan.
2. Feature.enable(:vsa_standalone_settings_page)
3. Visit any group that has VSA data or follow these steps:
   1. run FILTER=cycle_analytics SEED_VSA=1 bundle exec rake db:seed_fu
   2. Visit the group's VSA. The group URL is present in the output of the command above.
4. Navigate to http://{YOUR_LOCAL_INSTANCE}/groups/{GROUP_PATH}/-/analytics/value_stream_analytics/value_streams/new and verify that the page works and the header with the Create value stream action appears
5. Grab the ID of any value stream from your chosen VSA from the value of the query parameter value_stream_id and navigate to http://{YOUR_LOCAL_INSTANCE}/groups/{GROUP_PATH}/-/analytics/value_stream_analytics/value_streams/{VALUE_STREAM_ID}/edit. Verify that the header with the edit actions appears.

Related to #381002 (closed)