docs: garbage collection proposal

This is the proposal for the new garbage collection functionality. It
was written post implementation to make sure we captured the intent of
the change and to aid with the review.

Even though its written post implementation it may merge first as the gc
work has been split into smaller PRs to aid review.

Signed-off-by: Richard Case <[email protected]>

Author: richardcase

docs/proposal/20220712-garbage-collection-create.plantuml

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+@startuml
+autonumber
+actor User
+database APIServer
+control InfraClusterController
+participant gc_service
+collections other_services
+participant aws
+User -> APIServer: apply capi yaml
+InfraClusterController -> APIServer: watch (create/update)
+activate InfraClusterController
+InfraClusterController -> InfraClusterController: Add infra cluster finalizer
+opt if gc feature enabled
+    InfraClusterController -> gc_service: Reconcile
+    opt if gc annotation != false
+    else
+        gc_service -> gc_service: add gc finalizer
+    end
+end
+InfraClusterController -> APIServer: patch infracluster
+InfraClusterController -> other_services: Reconcile
+other_services -> aws: create cluster infra
+other_services -> InfraClusterController: update status
+InfraClusterController -> APIServer: patch
+deactivate InfraClusterController
+@enduml

docs/proposal/20220712-garbage-collection-create.svg

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+@startuml
+autonumber
+actor User
+database APIServer
+control CAPIController
+control InfraClusterController
+participant gc_service
+collections other_services
+participant network_service
+participant aws
+User -> APIServer: delete cluster
+CAPIController -> APIServer: watch
+activate CAPIController
+CAPIController -> APIServer: delete infra (set timestamp)
+
+InfraClusterController -> APIServer: watch (delete)
+activate InfraClusterController
+InfraClusterController -> other_services: Reconcile Delete 
+other_services -> aws: Delete non-network infra
+opt if InfraCluster has gc finalizer
+    InfraClusterController -> gc_service: ReconcileDelete
+    gc_service -> aws: Delete tenant created resources (lb/sg)
+    gc_service -> gc_service: remove gc finalizer
+    gc_service -> APIServer: patch infracluster
+end
+InfraClusterController -> network_service: Reconcile Delete
+network_service -> aws: delete network infra
+InfraClusterController -> InfraClusterController: Remove infra finalizer
+InfraClusterController -> APIServer: patch
+deactivate InfraClusterController
+deactivate CAPIController
+APIServer -> APIServer: Delete infra cluster
+
+@enduml