This PR adds a make mdlint_fix target that will run markdownlint. This is a convenience target for SSVC developers to clean up markdown changes prior to submitting PRs, since we're checking for that in one of our PR workflows.

CoPilot Summary

This pull request includes updates to the Makefile to add a new target for fixing markdown linting issues. The most important changes are:

• Added a new target mdlint_fix to the Makefile that runs markdownlint with the --fix option to automatically correct markdown linting issues.
• Updated the help section in the Makefile to include a description for the new mdlint_fix target.