Add MIT license

In order to clearly cover the legal usage of this cookbook, this commit
updates the metadata file to state that this cookbook is released under
the MIT license. As well, it updates the license file to reflect the
text of the MIT license.

[24818]
Merge pull request #26 from sqm/24818-update-license-for-rubycas

#24818 - Add MIT license
Merge branch 'master' into 24820-remove-gemfilelock-from-gitignore-in-rubycas

* master:
  Add MIT license

Conflicts:
	metadata.rb