Add pomfirst build + add K3FSM example MEP server

[dvojtise]

This PR contributes to the addition of a Model Execution Protocol implementation in GEMOC.

The generic part of the MEP framework is contained in https://github.com/eclipse/gemoc-studio-modeldebugging/pull/169 and a specific implementation for K3 is contained in https://github.com/eclipse/gemoc-studio-execution-java/pull/7.

This PR :

• adds a new pomfirst build entry point in dev_support/pomfirst/pom.xml allowing to build all GEMOC pomfirst projects in a single command (similar to dev_support/full_compilation/pom.xml that applies to tycho based builds)
• adds a Model Execution Protocol server project to the K3FSM official example as an example of the K3MEP server of https://github.com/eclipse/gemoc-studio-execution-java/pull/7. Ie. It implements the org.eclipse.gemoc.executionframework.mep and org.eclipse.gemoc.execution.sequential.javaengine.headless by connecting the K3FSM dsl to the engine and presents it via a quarkus based websocket server. (this example should not be here but this is another issue https://github.com/eclipse/gemoc-studio/issues/210)