Add towncrier for automatic changelog generation (#10379)

blast from the past! resurrects
https://github.com/certbot/certbot/pull/9803 with all of @bmw's changes.
i figured instead of force-pushing a basically brand new branch and
obliterating the old review, i'd just start from a clean slate

fixes #8272

---------

Co-authored-by: Brad Warren <bmw@users.noreply.github.com>
Co-authored-by: Brad Warren <bmw@eff.org>

towncrier.toml

@@ -0,0 +1,26 @@
+[tool.towncrier]
+package = "certbot"
+directory = "newsfragments"
+filename = "certbot/CHANGELOG.md"
+title_format = "## {version} - {project_date}"
+issue_format = "[#{issue}](https://github.com/certbot/certbot/issues/{issue})"
+issue_pattern = "\\d+"
+wrap = true
+ignore = []
+
+# Our three custom news fragment types, declared in order of how we'd like them
+# to appear in the changelog
+[[tool.towncrier.type]]
+directory = "added"
+name = "Added"
+showcontent = true
+
+[[tool.towncrier.type]]
+directory = "changed"
+name = "Changed"
+showcontent = true
+
+[[tool.towncrier.type]]
+directory = "fixed"
+name = "Fixed"
+showcontent = true