Allow access to review apps for all developers and designers

[bartjkdp]

Mentioned by @boris-arkenaar

• There is currently a hard dependency on the Amsterdam identity management and acceptance backend for Netlify review apps.
• We would like all developers and designers involved with Signalen to be able to login to review apps.

Possible solution direction

• Use / create a separate review cluster (at VNG?) that we can use to spin up environments (frontend and backend) dynamically per feature branch or setup a fixed identity provider and acceptance backend. Have a look at Github Actions for deploying to Kubernetes Service.
• Use Github Single Sign On using the Signalen organisation via Dex.