feat(java17): compile with JDK17 targeting Java 11 bytecode

[mattgogerly]

DO NOT MERGE PRE-1.33

• Swap the setup-java versions around so that 17 comes first on the PATH.
• Update build commands to enable cross compilation plugin.

Build should pass once spinnaker/spinnaker-gradle-project#203 and spinnaker/spinnaker-gradle-project#204 are both merged.

Confirmed it's working with targetJava17=false:

javap -v igor-web/build/classes/groovy/main/com/netflix/spinnaker/igor/Main | grep major
Warning: File ./igor-web/build/classes/groovy/main/com/netflix/spinnaker/igor/Main.class does not contain class igor-web/build/classes/groovy/main/com/netflix/spinnaker/igor/Main
  major version: 55

and true:

javap -v igor-web/build/classes/groovy/main/com/netflix/spinnaker/igor/Main | grep major
Warning: File ./igor-web/build/classes/groovy/main/com/netflix/spinnaker/igor/Main.class does not contain class igor-web/build/classes/groovy/main/com/netflix/spinnaker/igor/Main
  major version: 61

[dbyron-sf]

Is the idea to wait on merging this until 1.33 appears?

[mattgogerly]

Is the idea to wait on merging this until 1.33 appears?

Correct, just trying to figure out what needs fixing now to get a headstart.