[FEAT]: howto: Add howto-install-eclipse-capella

[gmacario]

📑 Description

Eclipse Capella™ is an Open Source solution for Model-Based Systems Engineering. This PR adds a new HOWTO which explains how to install the program and use it for the ARNEIS project.

NOTE: This is an early draft of the HOWTO, looking forward to future contribution by other people who are more knowledgeable with Eclipse Capella than myself.

✅ Checks

• [x] My pull request adheres to the code style of this project
• [x] My code requires changes to the documentation
• [x] I have updated the documentation as required
• [x] All the tests have passed

ℹ Additional Information

[gmacario]

@alv67 kindly review and merge the PR. Thanks!