Fix header issue in subpages.

Fix inconsistent header issue in webpage

Description

In the previously built UNICADO website, many pages had inconsistent headers. This commit aims to address the issue by leveraging mkdoxy documentation. Initially, only propulsion_design-related files have been modified to test this approach. If successful, the solution can be extended to all other subpages to resolve the header inconsistency problem.

Related Issue(s)

• Fixes #22

Testing Instructions

1. [Step 1: checkou branch documentation/global-header-file-setup]
2. [Step 2: Run command mkdocs build --site-dir ./public and mkdocs serve]
3. [Step 3: Go to page propulsion_designand verify the result]

Developer Checklist

• Code has been tested locally and/or in pipeline.
• (if applicable) documentation updated.
• (if applicable) impact of new dependencies reviewed and included in project.
• Merge conflicts resolved with the target branch.