Set up H2 in-memory database for development and testing with directory instructions

[merxgrc]

Summary:
Set up H2 as an in-memory database for the Java Spring API project to facilitate easier development and testing.

Tasks:

• Add the H2 database dependency to the pom.xml file in the project's root directory.
• Configure the H2 database settings by editing the src/main/resources/application-dev.properties and src/main/resources/application-test.properties files. Add the following properties:

  spring.datasource.url=jdbc:h2:mem:testdb
  spring.datasource.driverClassName=org.h2.Driver
  spring.datasource.username=sa
  spring.datasource.password=
  spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
  spring.h2.console.enabled=true

• Make sure the H2 console is enabled and accessible at /h2-console for dev and test profiles.
• Update the DEV_README.md with a new section titled "Development Database" that explains how to use the H2 database and access the console.

Acceptance Criteria:

• The application starts with H2 in-memory database for dev and test profiles.
• The H2 console is accessible via browser at /h2-console.
• Instructions for usage are clear in the documentation.