[Snyk] Upgrade gatsby-plugin-mdx from 2.6.0 to 2.15.0#388

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

snyk-upgrade-ffafa815ccd006636414762ca696df9eibm-self-serve-assets/ibm-gsi-cloudnative-journey:snyk-upgrade-ffafa815ccd006636414762ca696df9eCopy head branch name to clipboard