Automate PR Header Checks & Disallow multiple empty lines

[cicoyle]

We should add a github actions workflow or similar that runs on every PR and checks whether the files include the required license header block.

[salaboy]

100%, @cicoyle do you know if we have this for other SDKs? or even dapr/dapr?

[cicoyle]

We don't in runtime. I'm uncertain about other SDKs. We should generally include this across all repos. I can open up follow up issues in the other repos.

[siri-varma]

/assign