Use Towncrier for the changelog and convert it to Markdown

[abompard]

Follow the cookiecutter template with changelog management:

• use towncrier to generate it
• convert it to markdown
• have it be picked up by the Github action on tag/release to generate the Github release notesFollow the cookiecutter template with changelog management:
• use towncrier to generate it
• convert it to markdown
• have it be picked up by the Github action on tag/release to generate the Github release notes