chore(dependencies): add rxjava to compile classpath (#4738)

thanks groovy... I guess without rxjava on compile (even though it is in runtime) the controllers that are
using it are compiling to some groovy methodMissing metagarbage...

clouddriver-web/clouddriver-web.gradle

@@ -43,6 +43,7 @@ dependencies {
   implementation("com.netflix.spinnaker.kork:kork-plugins")
   implementation "com.netflix.spinnaker.moniker:moniker"
   implementation "commons-io:commons-io"
+  implementation "io.reactivex:rxjava"
   implementation "io.swagger:swagger-annotations"
   implementation "org.codehaus.groovy:groovy-all"
   implementation "org.slf4j:slf4j-api"