managed_modules.yml: sort modules alphabetically

[bastelfreak]

No description provided.

[jhoblitt]

Maybe we should add some rspec to check that the list is sorted?

[kenyon]

Note that order depends on how the sort is implemented. For example, Visual Studio Code's built-in sort function works differently than the coreutils sort command: microsoft/vscode#48123

So it would be good to have a standard way of doing it, like with a rake task, and a verification method, like @jhoblitt says.

[jhoblitt]

I have a close enough copy of coreutils sorting behavior to use it in a spec file. https://github.com/lsst-it/lsst-control/blob/production/spec/unit/puppetfile_spec.rb