Add context to the go-server generated code

Created by: randomswdev

PR checklist

• Read the contribution guidelines.
• If contributing template-only or documentation-only changes which will change sample output, build the project before.
• Run the shell script(s) under ./bin/ (or Windows batch scripts under.\bin\windows) to update Petstore samples related to your fix. This is important, as CI jobs will verify all generator outputs of your HEAD commit, and these must match the expectations made by your contribution. You only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the code or mustache templates for a language ({LANG}) (e.g. php, ruby, python, etc).
• File the PR against the correct branch: master, 4.3.x, 5.0.x. Default: master.
• Copy the technical committee to review the pull request if your PR is targeting a particular programming language.

Update the go-server code genertor in order to:

1. return 400 in case of an invalid input parameter (very likely is not an internal error).
2. use baseName instead of paramName when gettin a parameter from maps (this makes difference for a parameter like "user-id")
3. pass the ctx to the called handlers, so that they can take decisions based on the calling context and propagate it in ase of down calls.
4. allow handlers to return a status code. And handler that creates a resource should be allowed to return HTTP 201 instead of HTTP 200.
5. allow an handler to return a reponse function in order to fully customize the response. This is useful when, for example, redirecting a requestor; in this case both a custom state and custom headers have to be returned.

@antihax @bvwells @grokify @kemokemo @bkabrda please review.