Integrate spring-data/* generators into spring-boot.

[mshima]

Overview of the feature request

Spring Data Starters are part of Spring Boot project, I think spring-data/* generators should be moved into spring-boot generator.

Example:
spring-data:cassandra -> spring-boot:data-cassandra

Motivation for or Use Case

Related issues or PR

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[sams52s]

hi, i would like to contribute to this task. @mshima

[mshima]

@sams52s please go ahead.