fix: fix concurrency issue

[FreddyDevelop]

Description

With current implementation of the flow builder and how it is used, each request shared the same flow instance, this leads to a concurrency issue, because the flow instance holds the database transaction and http context of a request. And when all incoming request share the same flow instance, the transaction and http context get overridden and also we get a concurrency write error on the contextValue variable in the flow.

Implementation

Create a new instance of a flow for each incoming request. The scanFlowStates function from the defaultFlowBuilder is changed, that this only runs once.

Tests

Call an endpoint e.g. /registration automated (concurrent) many times (at least one action should be used e.g. register_client_capabilities). Check that no errors occur.