doc(arch): added proposal for new infrastructure provisioning hierarchy

docs/technical-documentation/architecture/decisions/environment-hierarchy.md

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+# proposal: how to (re)structure our infrastructure setup
+
+what we have:
+* different providers - currently OTC and kind
+* different groups of environments - currently called 'environment_namespace'
+* different environments in each group of environments
+* environments are called 'cluster_environment' and are terragrunt stacks, i.e. a huge set of resources where the kubernetes cluster itself is only one of them
+* the top domain name (like t09.de, buildth.ing) is bound to the environment group
+
+issues:
+* in provider OTC there are two attributes for the environment group - 'tenant' and 'environment_namespace' are the same 
+* missing hierarchy for other providers than otc - we directly start with 'prod' and 'non-prod' right now
+
+## opportunity
+
+right now we start switching to go code.
+we can use this port to also restructure, generalize and improve the infrastructure and platfrom-provisioning.
+
+
+## proposed environment hierarchy
+
+* new: the 'environment_namespace' layer is called 'platformzone': "A neutral, abstract term that encompasses both the isolation (account, tenant, subscription) and the operational context (prod vs. non-prod)." (ChatGPT)
+* new: folder 'environments'
+* new: level 1 hierarchy 'provider'
+* old: level 2 hierarchy 'platformzone'
+* old: level 3 hierarchy 'environment'
+
+### visualization
+
+```bash
+environments
+├── provider:kind
+│   └── platformzone:non-prod e.g.vm-1 or local
+│       ├── edp
+│       └── observability
+├── provider:otc
+│   ├── platformzone:non-prod i.e. tenant-1
+│   │   ├── central-forgejo-aka-edp
+│   │   ├── forgejo-dev
+│   │   └── observability
+│   └── platformzone:prod i.e. tenant-2
+│       ├── edp
+│       └── observability
+└── provider:scaleway
+    ├── platformzone:non-prod e.g. account-1
+    └── platformzone:prod e.g. account-2
+        ├── edp
+        └── observability
+```