Update Architecture Documentation for 2.0

[mpstefan]

To reflect new architecture
Can we get a redraw of our diagram? Marketing help?
Update the pod readiness section

Acceptance

• The architecture documentation page is updated to reflect the new NGF architecture
  • The architecture diagram is updated
  • The pod readiness section is updated to reflect the new architecture
  • The NGINX Gateway Fabric pod section is rewritten with an updated diagram

[mpstefan]

@ciarams87 Should include how if the control plane goes down, the data plane does not and vise versa.