MEND OSS Scanning GitHub app for main repositories

## Story
As a Galasa devloper, I want the MEND GitHub app to scan the OSS dependencies in my repositories, so that I can be notified of security vulnerabilities in OSS as soon as they are introduced.

## Tasks
- [ ] Review the documentation for [MEND for GitHub](https://docs.mend.io/integrations/latest/mend-for-github-com)
- [ ] Configure on the galasa repository
