Merge duplicate instructions on GCP onboarding, roles, service enablements, billing and bootstrap project - continuation of 362

[obriensystems]

PR additionally upstream via terraform-google-modules/terraform-example-foundation#1204

specifically the prerequisites sections with roles and service enablements duplicated across
"For the user who will run the procedures in this document, grant the following roles:"
and
"Enable the following additional services on your current bootstrap project"

https://github.com/GoogleCloudPlatform/pbmm-on-gcp-onboarding/blob/main/0-bootstrap/README.md#prerequisites
https://github.com/GoogleCloudPlatform/pbmm-on-gcp-onboarding/blob/main/0-bootstrap/README-Terraform-Cloud.md#requirements
https://github.com/GoogleCloudPlatform/pbmm-on-gcp-onboarding/blob/main/0-bootstrap/README-GitLab.md#deploying-a-gitlab-cicd-compatible-environment
https://github.com/GoogleCloudPlatform/pbmm-on-gcp-onboarding/blob/main/0-bootstrap/README-GitHub.md#requirements

no section in
https://github.com/GoogleCloudPlatform/pbmm-on-gcp-onboarding/blob/main/0-bootstrap/README-Jenkins.md

Check each terraform module specific to the build agent - for example

• https://github.com/terraform-google-modules/terraform-example-foundation/blob/master/0-bootstrap/modules/jenkins-agent/README.md#Requirements

Fix:
detail all common roles and service enablements in the main readme, put links back to this readme from the extended readme's and add specific roles/services per gitlab/github/terraform-cloud/ado in extended readme's

see

• #362 - bootstrap prereq #363
• Add bootstrap project requirements / project service enablements / readme / sh scripting / super admin roles - in prep of running 0-bootstrap #362
• fix: Add roles and service enablements to bootstrap project terraform-google-modules/terraform-example-foundation#1175
• ER: Canadian Government Federal and Provincial Clients: Fortinet based hub-spoke Landing Zone terraform-google-modules/terraform-example-foundation#1133

[github-actions]

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