Add AppBootVersion to 'app register' shell/client

[onobc]

• Introduces the AppBootVersion enum
• Hooks into 'app register' shell command
• Passes boot version into AppRegistryController

See #5239

Steps to exercise

• build code in the branch w/ ./mvnw clean install -DskipTests
• start server w/ java -jar spring-cloud-dataflow-server/target/spring-cloud-dataflow-server-2.10.2-SNAPSHOT.jar
• start shell w/ java -jar spring-cloud-dataflow-shell/target/spring-cloud-dataflow-shell-2.10.2-SNAPSHOT.jar
• in shell register boot2 app w/o boot version

  dataflow>app register --type task --force --name timestamp --uri maven://org.springframework.cloud.task.app:task-timestamp:3.2.0
  

• in shell register boot2 app w/ boot version

  dataflow>app register --type task --force --name timestamp --uri maven://org.springframework.cloud.task.app:task-timestamp:3.2.0 --bootVersion 2
  

• in shell register boot3 app w/ boot version

  dataflow>app register --type task --force --name timestamp --uri maven://org.springframework.cloud.task.app:task-timestamp:3.2.0 --bootVersion 3
  

The output from the shell is as follows for boot2

Successfully registered application 'task:timestamp'

The output from the shell is as follows for boot3

Successfully registered application 'task:timestamp' (boot 3)

[corneil]

I would remove the prefixes and description from the enum. I've submitted a commit to your repo.

[onobc]

I would remove the prefixes and description from the enum. I've submitted a commit to your repo.

What is the benefit of moving the static information out of the enum? Ultimately it will be pulled into a row in the DB.