Add low level architecture diagrams to root readme

Update the architecture diagrams for unmanaged and managed versions of the lz

Update/refer to
- 20230325 deck https://docs.google.com/presentation/d/13sjT2tJ4yLIYGRREE3wBrylB1OvcEMpKdquVuJB_nX4/edit?resourcekey=0-N3DruQaiutFvZ98HTT7-vQ#slide=id.g1154b3b950f_2_3458
- 202212 deck https://docs.google.com/presentation/d/1Ztqn7G2rWFlssVwC7r5Xl-WFSFCbVo6MoHJffrXScmw/edit#slide=id.ga472c7d3d1_3_834
- dev branch lz v1 arch https://github.com/GoogleCloudPlatform/pubsec-declarative-toolkit/blob/dev/solutions/landing-zone/architecture.md#diagrams
- gcp-documentation https://github.com/ssc-spc-ccoe-cei/gcp-documentation/blob/main/Architecture/Repository%20Structure.md