📣 Start managing the changelog with towncrier

This PR includes a workflow that validates that future PRs include
a changelog entry (unless the `skip-changelog` label is present on the
PR, or the PR is a dependabot PR).

Use 'poetry run towncrier create` to create entries for the changelog.

changelog.d/changelog_template.jinja

@@ -0,0 +1,15 @@
+{% if sections[""] -%}
+{% for category, val in definitions.items() if category in sections[""] -%}
+
+### {{ definitions[category]['name'] }}
+
+{% for text, values in sections[""][category].items() %}
+- {{ text }} {{ values|join(', ') }}
+{% endfor %}
+
+{% endfor -%}
+{% else -%}
+No significant changes.
+
+
+{% endif -%}