Add new property "config-key" and use configKey instead openApiSpecId on templating

[mcruzdev]

This pull request try to fix the issue #363

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[ricardozanini]

Many thanks for your contributions! I have a few observations if you don't mind reviewing.

[ricardozanini]

Thank you! I think we are getting in there! 👯

[hbelmiro]

Thank you @mcruzdev. Good job!
I left a few picky comments and it seems you forgot to create some tests (see the comments).