Default branch migration from master to main

We will be migrating the default branches of all feedstocks and other conda-forge repos from master to main. We do expect some minor hiccups while this migration is going on. You will need to change to the main branch from master on any local clones via the following git commands:

git branch -m master main
git fetch origin
git branch -u origin/main main
git remote set-head origin -a

If you encounter any problems, please comment on this Github issue.