Allow additional configuration of API Server

[Zetten]

No description provided.

[scotty-c]

@Zetten The code looks good. Can you give me an example of what you would add as an extra param.
I will update the readme and changelog after the merge

[Zetten]

The driver for this in our environment was integration of an authentication provider, in our case Dex. Hooking this up so that users can get and use bearer tokens with kubectl requires extra API Server parameters.

Configuring puppetlabs-kubernetes (using hiera) to connect with Dex looks like:

kubernetes::apiserver_extra_arguments:
  - --oidc-issuer-url=https://dex.example.com:32000
  - --oidc-client-id=example-app
  - --oidc-ca-file=/etc/kubernetes/ssl/openid-ca.pem
  - --oidc-username-claim=email
  - --oidc-groups-claim=groups

[scotty-c]

@Zetten Perfect, thanks heaps for your contribution