Use real report fixtures instead of mockData.js

Instead of maintaining the mock-files in this big javascript file ee/spec/javascripts/vue_shared/security_reports/mock_data.js, we should make use of the real json files we have. For example:

• for 11.6: https://gitlab.com/gitlab-org/security-products/dependency-scanning/blob/v1.4.0/test/expect/gl-dependency-scanning-report.json

• for 11.7: https://gitlab.com/gitlab-org/security-products/dependency-scanning/blob/ee-8747/test/expect/gl-dependency-scanning-report.json

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The following discussion from !8869 (merged) should be addressed:

• @psimyn started a discussion: (+1 comment)

  is it possible to generate this as fixture, or overly difficult? I'm trying to cut back on mock_data additions