yamlfmt (#4587)

* Added the fixer, wrote tests and tested it

autoload/ale/fix/registry.vim

@@ -179,7 +179,12 @@ let s:default_registry = {
 \   'yamlfix': {
 \       'function': 'ale#fixers#yamlfix#Fix',
 \       'suggested_filetypes': ['yaml'],
-\       'description': 'Fix yaml files with yamlfix.',
+\       'description': 'Fix YAML files with yamlfix.',
+\   },
+\   'yamlfmt': {
+\       'function': 'ale#fixers#yamlfmt#Fix',
+\       'suggested_filetypes': ['yaml'],
+\       'description': 'Format YAML files with yamlfmt.',
 \   },
 \   'yapf': {
 \       'function': 'ale#fixers#yapf#Fix',