ci: Add semantic release templates

Add templates for the release notes and `CHANGELOG` so
`python-semantic-release` can generate these files correctly in CI.

Author: jmgate

templates/.release_notes.md.j2

@@ -0,0 +1,11 @@
+{% for type_, commits in release["elements"] | dictsort %}
+### {{ type_ | capitalize if type_ != "ci" else "Continuous Integration" }}
+{%- if type_ != "unknown" %}
+{% for commit in commits -%}
+{%- set summary = commit.message.rstrip().splitlines()[0] -%}
+{%- set details = commit.message.rstrip().splitlines()[2:] -%}
+* {{ summary }} ([`{{ commit.hexsha[:7] }}`]({{ commit.hexsha | commit_hash_url }}))
+{% if details %}
+{% for line in details %}{% if line.strip() %}  {{ line }}{% endif %}
+{% endfor %}{% endif -%}
+{% endfor %}{% endif %}{% endfor %}

templates/CHANGELOG.md.j2

@@ -0,0 +1,15 @@
+# CHANGELOG
+
+
+{% for version, release in context.history.released.items() %}
+## {{ version.as_tag() }} ({{ release.tagged_date.strftime("%Y-%m-%d") }})
+{% for type_, commits in release["elements"] | dictsort %}
+### {{ type_ | capitalize if type_ != "ci" else "Continuous Integration" }}
+{% for commit in commits -%}
+{%- set summary = commit.message.rstrip().splitlines()[0] -%}
+{%- set details = commit.message.rstrip().splitlines()[2:] -%}
+* {{ summary }} ([`{{ commit.hexsha[:7] }}`]({{ commit.hexsha | commit_hash_url }}))
+{% if details %}
+{% for line in details %}{% if line.strip() %}  {{ line }}{% endif %}
+{% endfor %}{% endif -%}
+{% endfor %}{% endfor %}{% endfor %}