Feature/dynamic accounts setup (#2)

[Fatema]

Issue #, if available:

Description of changes:

• update README for infra repository

• update READMEs and the diagrams

• remove some constant values

• removing loaded account ids from config

• add new template option for dynamic accounts through cfn params

• add more to README

• rename stagin to preprod

• remove space from folder name

• remove account specific details

• add comments to constants.py

• update script to handle updating constants.py

• adding minor detail

Co-authored-by: Fatema Alkhanaizi alkhanai@amazon.co.uk

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[georschi]

Thanks for the updates!