Make the ShortenerTool.Core a completed package

[fboucher]

The idea is to move all the logic into ShortenerTool.Core, without any security check. This way we could create multiple wrapper that implement the security we need (or none) depending on the context and usage.
It could be a NuGet package and be easy to integrate in many projects. We could finally work on the CLI we've been dreaming about for so long.

Any thoughts? Feedback? Warning? Push-back?

[fboucher]

I create a draft PR for this #506

• code Cloud5mins.ShortenerTools.Core
• code Cloud5mins.ShortenerTools.Function
• code Cloud5mins.ShortenerTools.FunctionLight
• deployment (in progress)
• documentation

Note: this new version will allow the free SWA plan again 🥳