Cauldron/manifest repo clone reference explicit default branch

[friederbluemle]

Many command in ern core have a hardcoded reference to the master branch. If a different branch name is used, it can cause confusion and/or require unnecessary configuration on the consumer side. Git operations should simply using the default branch (as set by origin/HEAD) by default, which will avoid the need to explicitly name a branch and make the commands work in a more generic way.