feat: Support for .NET Core Function Apps

[tbarlow12]

What did you implement:

Support for .NET Core Function apps using .NET Core 2.2 or 3.1 on both Windows and Linux

Closes #367

How did you implement it:

• Created CliCommandFactory to centralize all commands that will be spawned as child processes
• Unified configConstants and constants (this is why there are so many files changed)
• In the package plugin, detects if the runtime is a "compiled" runtime (C#, potentially Java and others), and in that case, replaces the native Serverless packaging hook with a compileArtifact hook, which spawns a process to compile the artifact and put it in the .serverless directory
• Package Service now cleans up any folders generated by the C# build as well

How can we verify it:

• I will be creating a template in the next PR that will contain integration tests. Use that template and deploy your own :)

Todos:

Note: Run npm run test:ci to run all validation checks on proposed changes

• Ensure there are no lint errors.
  Validate via npm run lint
  Note: Some reported issues can be automatically fixed by running npm run lint:fix
• Write tests and confirm existing functionality is not broken.
  Validate via npm test
• Write documentation
• Provide verification config / commands / resources
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

Is this ready for review?: YES
Is it a breaking change?: NO

[aguywithcode]

This is beautiful...thanks for picking this up!

[updateaman]

@tbarlow12 thank you for this. Did you manage to create the template for using .Net Core Functions?