Write ADR about no state machine dependency

packages/dito/doc/adr/0004-no-state-machine-dependency.md

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+# 4. Do not use an external dependency as state machine
+
+Date: 2024-05-21
+
+## Status
+
+Accepted
+
+## Context
+
+The digital touchpoint application will feature a dialog form that guides users through a series of questions.
+We need to decide whether to use an external dependency, such as [xstate](https://xstate.js.org/),
+which provides a state machine implementation, or to implement the flow ourselves. The application
+will ask users a fixed number of questions (currently five), with a set order and no conditional
+logic for skipping questions. This setup is not expected to change in the near future.
+The answers will determine different outcomes on a result page.
+
+The benefits of using an external state machine dependency include:
+
+- Easier addition of new questions or changes to the order once set up
+- Improved management of complexity if the dialog form evolves, reducing the risk of errors and minimizing code changes
+
+However, there are also some drawbacks:
+
+- Introducing a dependency adds maintenance work and increases the software’s complexity and size
+- The mental model of the dependency must be understood
+- Learning to use the dependency requires additional effort
+
+## Decision
+
+We do not use an external dependency as a state machine, as it would introduce unnecessary overhead given the
+current simplicity of the dialog form.
+
+## Consequences
+
+We will implement our own dialog form flow for the five consecutive questions without relying on an external dependency.
+
+We will reassess this approach if the complexity of the dialog form increases.