[4.x] Helidon Data examples

[Tomas-Kraus]

Contains 3 examples for Helidon Data:

• SE imperative
• SE declarative
• MP

Added MethodName checkstyle suppression for examples/data/, examples/declarative/data/ and examples/microprofile/data/ because required QbMN method name must contain '_' character.

[romain-grecourt]

Directory structure:

• SE examples go at the top level
• MP examples go under microprofile
• Declarative examples go under declarative

Avoid the se, mp suffixes / prefixes.

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Keep the examples simple, with a small number of classes:

• Single entity
• Single table
• Single HTTP endpoint
• Single Java package, if possible

Ideally, a basic Helidon Data CRUD example has only 3 classes:

• the JPA entity
• the Repository class
• the HTTP service class.

Anything advanced (E.g. transaction) should go in separate examples.

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The existing database examples have been updated recently, make sure you align with those.

• https://github.com/helidon-io/helidon-examples/tree/fbfe2fb21f9c9564c916642705a1c2144ce3210d/examples/dbclient
• https://github.com/helidon-io/helidon-examples/tree/fbfe2fb21f9c9564c916642705a1c2144ce3210d/examples/integrations/cdi/jpa
• https://github.com/helidon-io/helidon-examples/tree/fbfe2fb21f9c9564c916642705a1c2144ce3210d/examples/integrations/cdi/datasource

The examples are duplicated per database, the current choices of databases is MySQL, Oracle, Postgres.

The examples implement the same identical CRUD application, based on the Pokemon theme.

The instructions in the README match the default configuration, the test uses Testcontainers to exercises the HTTP endpoint documented in the README.

Add-on (health, metrics, tracing) are implemented as separate examples.

[Tomas-Kraus]

This PR seems to be broken (git changesets were not updated). Moving to #210