Add content_source enum override + update java sdk

[fern-support]

• Adds an additional type to content_source, which fixes a previously failing test searchTest() in src/test/java/com/intercom/api/integration/ConversationsTest.java
• Points the java config in fern/generators.yml to the real repo (intercom/intercom-java) as of opposed to the fern-demo version
• Adds a workflow that publishes the Java SDK