Helidon MCP coffee shop examples

[tvallin]

Introduces two applications - Helidon MCP coffee shop and Helidon MCP coffee shop declarative.

They show case how to set up a Helidon MCP server and a few Helidon data features. The examples provides three tools:

• Customers can ask for the coffee shop menu. The menu is stored in the in-memory database (H2) and created at startup using the init.sql script.
• Customers can then take an order. An order is defined by the customer name, the list of menu items and the total price.
• Customer can ask what are the current orders. The orders are also in the H2 database and given to the customer where he can unsure that his order was taken successfully.

Both examples mirror each others in terms of functionality, but one uses an imperative approach where the other uses declarative. A user can see what differences and changes are required for writing the same application using both ways.

The two applications are covered with tests, a Langchain4j client is used to initialize a connection with the MCP server and exercise the MCP specific method required to use the app.

This PR adds a new directory under apps named mcp where the two applications are located.