Improves fast/data-platform-ng README for clarity (#3074)

* Improves Data Platform README for clarity

* Quick fix to table of contents capitalization

* Fix broken link to stages README.md

* Fix broken link to stages README.md

* Add 2 diagrams.

* Update README.

* Update README.

* Fix section headings in README for consistency

* Clarify implementation details in README regarding Data Mesh principles and FAST stage integration

* Reposition folder structure diagram

* Remove Resource Hierarchy Overview section from README

* Remove diagram_resman.png from data platform development stage

* Update diagrams in README for Data Platform stage

* Refine descriptions of logical components in Data Platform architecture

* Refine README and configuration files for Data Platform stage, enhancing clarity and consistency in descriptions and structure.

* Add section for Provider and Terraform variables in README

* Remove demo files and configurations for Data Platform stage

* Fix file paths in IAM management references in README

* Add IAM principal for dp-platform and update resource counts in test files

* Update README to fix folder structure diagram order and alignment

* Fix capitalization and team naming inconsistencies in README

* Add note on IAM permissions review for production deployment in README

* Refactor IAM roles for dp-platform group in terraform.tfvars.sample

* Fix bucket name in product-0.yaml from 'exposed-ew8' to 'exposed'

---------

Co-authored-by: lcaggio <lorenzo.caggioni@gmail.com>
Co-authored-by: Ludovico Magnocavallo <ludomagno@google.com>

tests/fast/stages/s3_data_platform_dev/simple.tfvars

@@ -18,6 +18,7 @@ factories_config = {
       data-consumer-bi = "group:gcp-consumer-bi@example.com"
       dp-product-a-0   = "group:gcp-data-product-a-0@example.com"
       dp-domain-a      = "group:gcp-data-domain-a@example.com"
+      dp-platform      = "group:dp-platform-0@example.com"
     }
   }
 }

tests/fast/stages/s3_data_platform_dev/simple.yaml

@@ -24,7 +24,7 @@ counts:
   google_folder: 2
   google_folder_iam_binding: 3
   google_project: 3
-  google_project_iam_binding: 22
+  google_project_iam_binding: 23
   google_project_iam_member: 13
   google_project_service: 18
   google_project_service_identity: 6
@@ -38,4 +38,4 @@ counts:
   google_tags_tag_key: 1
   google_tags_tag_value: 1
   modules: 19
-  resources: 109
+  resources: 110