Use GraphQL-API to fetch security training providers

What does this MR do and why?

This MR adds changes that moves from client-side resolvers (with mock data), for retrieving security training providers, to fetching the data from the actual GraphQL endpoint.

It also contains the renaming of a Vue-injected value to have it consistent with the vulnerability report.

Screenshots or screen recordings

How to set up and validate locally

Setup

Enable the feature flag:

echo "Feature.enable(:secure_vulnerability_training)" | rails c

Create two training providers:

echo "Security::TrainingProvider.create!(name: 'Foo', description: 'Foo provider', url: 'http://foo.com', logo_url: [http://foo.com/logo')" | rails c

echo "Security::TrainingProvider.create!(name: 'Bar', description: 'Bar provider', url: 'http://bar.com', logo_url: 'http://bar.com/logo')" | rails c

1. Go to a project's "Security & Compliance" -> "Configuration"
2. Click on "Vulnerability Management"
3. Verify that both the "Foo" and "Bar" providers are visible (not configurable yet - will be tackled in separate issues)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #350956 (closed)