[BEAM-8106] Add Java 11 container to release and Java 11+V2+Dataflow testing

[emilymye]

• Fix java11 container task to actually output a java 11 container (whoops)
• Add ValidateRunner and Example postcommits against the container
• Add java11 container to release scripts

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Post-Commit Tests Status (on master branch)

Lang	SDK	Dataflow	Flink	Samza	Spark	Twister2
Go		---		---		---
Java
Python				---		---
XLang				---		---

Pre-Commit Tests Status (on master branch)

---	Java	Python	Go	Website	Whitespace	Typescript
Non-portable
Portable	---		---	---	---	---

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GitHub Actions Tests Status (on master branch)

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[emilymye]

Run seed job

[emilymye]

Run Java 11 Examples on Dataflow Runner V2

[emilymye]

R: @TheNeuralBit
R: @kennknowles

After some investigation, I think this is actually the more reliable way created to run Java 11 tests against Java 8 Beam (based on conversation from an old PR - the WIPs mentioned there are closed PRs but the actual code was committed later on. We should go back and fix tests in either case.

To test locally, I ran

./gradlew :runners:google-cloud-dataflow-java:examplesJavaRunnerV2IntegrationTest 
  -PdisableSpotlessCheck=true
  -PcompileAndRunTestsWithJava11
  -PskipCheckerFramework
  -Pjava11Home=...
  -PdataflowProject="..."
  -PdataflowTempRoot="..."
  -PdockerImageRoot="..."