Reusable workflow for publishing flutter packages

[git-elliot]

Dart projects which uses generated files can specify build_runner: true in workflow parameters.
Added workflow that allows smooth publishing of flutter packages.

But when I run this workflow in my github actions it doesn't pass authentication.

Validating package...
Pub needs your authorization to upload packages on your behalf.
In a web browser, go to https://accounts.google.com/o/oauth2/auth?access_type=offline&approval_prompt=force&response_type=code&client_id=818368855108-8grd2eg9tj9f38os6f1urbcvsq399u8n.apps.googleusercontent.com&redirect_uri=http%3A%2F%2Flocalhost%3A33935&code_challenge=nuG0mkGHs1kpqcsxkZdt0qQaX6zdhbInIiFrgAC9ILw&code_challenge_method=S256&scope=openid+https%3A%2F%2Fwww.googleapis.com%2Fauth%2Fuserinfo.email
Then click "Allow access".
Waiting for your authorization...

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