[Snyk] Upgrade gatsby-plugin-mdx from 2.6.0 to 2.15.0#386

mjperrins wants to merge 1 commit intodev-advancedibm-self-serve-assets/ibm-gsi-cloudnative-journey:dev-advancedfrom

snyk-upgrade-d2ed82fef437f29ca456b1c2a291929dibm-self-serve-assets/ibm-gsi-cloudnative-journey:snyk-upgrade-d2ed82fef437f29ca456b1c2a291929dCopy head branch name to clipboard