Add spring boot demo application version 2.7.18

[KiKoS0]

• https://start.spring.io/ by default supports spring boot version 3.x. 3.x is not compatible with Java 8, so we downgraded the generated app to 2.7.18 which is compatible. https://www.marcobehler.com/guides/spring-and-spring-boot-versions
• We changed the toolchain for inngest-core to Java 8 so that Java 8 apps can consume it. This meant we couldn't use Java httpclient which was introduced in Java 11.
• We evaluated a couple of Http clients and went with OkHttp because its API resembles the Java 11 Http client the most (Other clients were Google Http client and Apache Http client)
• The current state is that the app syncs correctly to the dev server but when a function is called it fails on steps execution because of two issues that we'll be looking into next:

  Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Handler dispatch failed; nested exception is java.lang.NoClassDefFoundError: kotlin/enums/EnumEntriesKt] with root cause

java.lang.ClassNotFoundException: kotlin.enums.EnumEntriesKt
	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641) ~[na:na]
	at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188) ~[na:na]
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521) ~[na:na]
	at com.inngest.OpCode.<clinit>(Function.kt:26) ~[main/:na]
	at com.inngest.InngestFunction.call(Function.kt:124) ~[main/:na]
	at com.inngest.CommHandler.callFunction(Comm.kt:85) ~[main/:na]
	at com.inngest.springbootdemo.InngestController.handleRequest(InngestController.java:40) ~[main/:na]
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104) ~[na:na]
	at java.base/java.lang.reflect.Method.invoke(Method.java:578) ~[na:na]
	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205) 

• The second issue is that reified inline functions cannot be called from Java and step.run currently is.
  

  inngest-kt/inngest-core/src/main/kotlin/com/inngest/Step.kt

  Line 28 in e9a6a15

  inline fun <reified T> run(

[albertchae]

paired on this together, there are still some outstanding issues as detailed in the PR description but we figured out enough of the Java 8 compilation that we thought it was worth merging something now

[darwin67]

looks good.
could you add the command you use to run spring boot server before you merge?

[darwin67]

The current SDK standards are to no expose any of the handlers to the users, and they can either,

• mount our route onto their HTTP controller
• directly create the HTTP endpoint for them

I'd imagine Java will be the former, so the singleton shouldn't exist and only the controller should be there.

[albertchae]

looks good. could you add the command you use to run spring boot server before you merge?

we need to figure out this out still 😅 , for now we were just running via IntelliJ

EDIT: #15

[albertchae]

okhttp is licensed under Apache 2.0 https://github.com/square/okhttp/blob/master/LICENSE.txt