feat: create github k8s service account

[blucas]

What does this PR do?

Creates a service account that can be used by CI systems for authentication/authorization to the k8s cluster. Also includes a temporary workflow which demonstrates that the service account can authenticate to the cluster and is authorized to execute various operations on said cluster. This workflow does not need to be committed.

Related issues

Closes #65

Checklist before merging

• My code follows the style guidelines of this project.
• I have performed a self-review of my own code.
• I have checked the contributing document.
• I have checked the existing Pull Requests to see whether someone else has raised a similar idea or question.
• I have added tests that prove my fix is effective or that my feature works.
• I have upgraded the changelog according to the nature of the feature that I am adding to this Pull Request.

[LucaLanziani]

@blucas one for you ;)

➜  k8s-kurated-addons git:(feat/create-gh-k8s-service-account) make create-ci-service-account 
/bin/bash: line 1: ./scripts/create-ci-service-account.sh: Permission denied
make: *** [Makefile:96: create-ci-service-account] Error 126

EDIT: ignore me I might have to pull again :D
EDIT2: nope I'm on latest

[LucaLanziani]

@blucas another one please:

➜  k8s-kurated-addons git:(feat/create-gh-k8s-service-account) ✗ make create-ci-service-account
error: the path "manifests/gha-service-account" does not exist
make: *** [Makefile:96: create-ci-service-account] Error 1