fix: add markdown-include package to workflow and poetry

[gvauter]

Description

Adds the markdown-include package to the publish-docs GitHub workflow and poetry dev group.

Fixes #338

Type of change

• Bug fix (non-breaking change which fixes an issue)

How has this been tested?

• Ran poetry install --with dev localy

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[jpower432]

LGTM