Migrate to JHipster v8

[mraible]

According to jhipster/generator-jhipster#23449, JHipster v8 is getting close. We should migrate and make sure everything works correctly.

[asomov]

@sendilkumarn can you please help to identify the work to be done ?

[sendilkumarn]

@asomov I have started working on this branch https://github.com/jhipster/jhipster-kotlin/tree/v8.0.0

There are a quite a few changes in v8

• Server (WIP @sendilkumarn)
• Spring Cache
• Spring Data
• Spring WebSocket
• Generator tests
• Integration Tests
• Entity Server
• Entity
• Generator fixes
• GitHub actions

Feel free to take any item and work on this branch - https://github.com/jhipster/jhipster-kotlin/tree/v8.0.0

[mshima]

@sendilkumarn do you want some help on this?
generator-jhipster v7 -> v8 should be done before any source code change to simplify migration.