Dismiss security-training promo when enabling it

What does this MR do and why?

To prevent showing the promition banner for the security-training unnecessarily, this MR adds a GraphQL) mutation, which dismisses the callout when the related configuration is being touched.

Note: The callout - and he code within this MR - is only temporary and will be removed in the future.

Screenshots or screen recordings

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How to set up and validate locally

Environment preparations

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

Testing instructions

1. Go to a project's vulnerability report - make sure the banner is showing up
2. Open a new browser tab and go to the same project's security dashboard - make sure the banner is showing up
3. Go to the project's "Security & Compliance" -> "Configuration" -> "Vulnerability Management"
4. Enable a provider (todo: enter instructions on how to populate)
5. Refresh the vulnerability report and security dashboard - make sure the banner does not show up any more

Reset the dismissed callout (in case you want to test it more than once)

echo 'User.find_by(username: "root").callouts.find_by(feature_name: "security_training_feature_promotion").destroy' | rails c

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 #350442 (closed)