Setup release notes build using towncrier tool

doc/release_notes/index.md

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+Release notes
+=============
+
+[comment]: <> (towncrier release notes start)

doc/release_notes/index.template.jinja

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+{% for section, _ in sections|dictsort(by='key') %}
+{% set underline = "-" %}
+{% if section %}
+{{section}}
+{{ underline * section|length }}{% set underline = "-" %}
+
+{% endif %}
+{% if sections[section] %}
+{% for category, val in definitions|dictsort if category in sections[section]%}
+
+{{ definitions[category]['name'] }}
+{{ underline * definitions[category]['name']|length }}
+
+{% if definitions[category]['showcontent'] %}
+{% for text, values in sections[section][category]|dictsort(by='value') %}
+- {{ text }}
+{% endfor %}
+{% else %}
+- {{ sections[section][category]['']|sort|join(', ') }}
+
+
+{% endif %}
+{% if sections[section][category]|length == 0 %}
+
+No significant changes.
+
+
+{% else %}
+{% endif %}
+{% endfor %}
+{% else %}
+
+No significant changes.
+
+
+{% endif %}
+{% endfor %}