GH-153 feat(repository): Added language property.

[Jamess-Lucass]

Closes #153

While language could be validated by checking against all the current options Bitbucket allows, there are a lot of languages they accept and I think it's appropriate to let Bitbucket handle the validation on language and to let terraform handle that error as such.

For example, when I change the language to something like invalid-lang and then apply the terraform configuration, this is the response.

[zahiar]

I'll merge this in & run the acceptance tests myself