[Golang] Support multiple APIKeys

[nmuesch]

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\. If contributing template-only or documentation-only changes which will change sample output, be sure to build the project first.
• Filed the PR against the correct branch: master, 4.1.x, 5.0.x. Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

Description of the PR

This PR aims to address #797 by adding multiple values to the Context attribute passed to authentication. This allows us to use a unique key to reference the Context with to retrieve any number of values for ApiKey

[wing328]

@nmuesch thanks for the PR. I wonder if you can update the Go (XML) petstore sample:

 // BasicAuth provides basic http authentication to a request passed via context using ContextBasicAuth
Perform git status
On branch pull/3210
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

	modified:   samples/client/petstore/go/go-petstore-withXml/api_fake_classname_tags123.go
	modified:   samples/client/petstore/go/go-petstore-withXml/api_pet.go
	modified:   samples/client/petstore/go/go-petstore-withXml/api_store.go
	modified:   samples/client/petstore/go/go-petstore-withXml/configuration.go

Script: ./bin/go-petstore-withxml.sh

[wing328]

Seems like this line is not indented correctly (1 additional tab)

[wing328]

And what about making ContextAPIKey a map instead as that's what we do in other languages?

[wing328]

Also the current implementation will result in compilation errors if the security name contains space or dash (e.g. "api key", "api-key")

[nmuesch]

Thanks for the input and review! I plan on getting back to this shortly and will give it another iteration.

[wing328]

@nmuesch just ping me via https://gitter.im if you need any help.

[wing328]

Please submit the change (breaking) against go-experimental generator instead.

Closing this one for the time being.