Move generate-platform-diagram.sh to a different place

Currently `generate-platform-diagram.sh` (the script to create the wiring-diagram) is placed at `swirlds-platform-core/src/main/java/com/swirlds/platform/wiring/generate-platform-diagram.sh`. We should move that to a folder that is not known by gradle (for example,` swirlds-platform-core/scripts`). `src/main/java` should never contain anything that is not a `*.java` file. Next to that all main src sets (src/main/*) are defined to be shipped. We do not want to have that script on every Hedera node.