Add relationships and reactive support to custom entity packages.

[mshima]

Followup to #16041.

• Change webflux workflow to allow a sample to use more than one JDL files.
  Having JDLs instead of .yo-rc.json and .jhipster/* entities is cleaner and easier to maintain.
• Split EntitySqlHelper class to a file, so it can be imported by another package.
• Create separated files-sql.json for modularity.

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[mshima]

@mraible should fix your jdl #16041 (comment)

[mraible]

I can confirm this fixes the problem, everything compiles, and e2e tests pass. As I was running these tests, I noticed that all the entity classes are generated at the root level and I thought to myself, "wouldn't it be cool if I could put all generated entity-related classes in their own sub-package?"

I tried @EntityPackage(app.blog) and @EntityPackage(app/blog) and neither of them work. Just wanted to make a note of this since others might think of this too.

[mshima]

I tried @EntityPackage(app.blog)

@mraible should work now using @EntityPackage("app.blog")

[mraible]

Double quotes works splendidly! 🎉

It looks like single quotes aren't supported:

Error during import-jdl: Error: unexpected character: ->'<- at offset: 319, skipped 1 characters.
Error: unexpected character: ->'<- at offset: 319, skipped 1 characters.

Here's the JDL I used to test:

application {
  config {
    baseName blog
    reactive true
    applicationType monolith
    authenticationType oauth2
    packageName com.jhipster.demo
    prodDatabaseType mysql
    cacheProvider ehcache
    buildTool maven
    clientFramework angular
    testFrameworks [cypress]
  }
  entities *
}

@EntityPackage("app.blog")
entity Blog {
  name String required minlength(3)
  handle String required minlength(2)
}

@EntityPackage("app.post")
entity Post {
  title String required
  content TextBlob required
  date Instant required
}

@EntityPackage("app.tag")
entity Tag {
  name String required minlength(2)
}

relationship ManyToOne {
  Blog{user(login)} to User
  Post{blog(name)} to Blog
}

relationship ManyToMany {
  Post{tag(name)} to Tag{entry}
}

paginate Post, Tag with infinite-scroll

[mraible]

Merging because this is a really cool feature.