docs: adds decision record about Java 17 (#401)

docs/development/decision-records/2023-05-23_java_17_baseline/README.md

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+# Java 17 baseline
+
+## Decision
+
+We will use Java 17 as baseline version.
+
+## Rationale
+
+Java 11 active support [will end in September 2023](https://endoflife.date/java), and, following Java "new" release cycle, we should update the baseline
+version to the current LTS from time to time.
+[EDC](https://github.com/eclipse-edc/Connector/blob/main/docs/developer/decision-records/2023-05-23-java-17-baseline/README.md) upstream is switching to Java 17.
+
+## Approach
+
+Remove the custom `javaVersion` and let the `edc-build` plugin set that when upgrading to the newest version of EDC.