[Snyk] Upgrade gatsby-plugin-mdx from 2.6.0 to 2.15.0#379

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

snyk-upgrade-97db43edf117b6034c9392861592f29dibm-self-serve-assets/ibm-gsi-cloudnative-journey:snyk-upgrade-97db43edf117b6034c9392861592f29dCopy head branch name to clipboard