feat: read platform secrets from Vault

mentioned in merge request example-service!148 (merged)

mentioned in merge request example-service!152 (merged)

mentioned in merge request docs!96 (closed)

mentioned in merge request docs!105 (merged)

mentioned in merge request gitlab-org/modelops/applied-ml/code-suggestions/ai-assist!1817 (merged)

mentioned in merge request gitlab-org/security-products/secret-detection/secret-detection-service!70 (closed)

mentioned in merge request gitlab-org/security-products/secret-detection/secret-detection-service!78 (merged)