General Issue: Add Copilot Instructions #2920
Description
Background Information
Add repo-specific instructions for Copilot
https://docs.github.com/en/copilot/how-tos/configure-custom-instructions/add-repository-instructions
These should reference Programming Strategy documents from {admiraldev}
https://pharmaverse.github.io/admiraldev/articles/programming_strategy.html
https://pharmaverse.github.io/admiraldev/articles/writing_vignettes.html
https://pharmaverse.github.io/admiraldev/articles/unit_test_guidance.html
Definition of Done
No response