add CHANGELOG

CHANGELOG.md

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+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+Since version unreleased the format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+This project (not yet) adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## unreleased

changelog/README.md

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+### Changelogs
+
+Temporary folder to add new changes. Each change should go into a separate file
+(unless it makes sense to group some changes into one file, e.g. a story).
+During release the changes will be moved to CHANGELOG.md.
+
+Each file should follow one of the below naming patterns:
+
+- \<issue number>.md
+  or
+- \<story number>.md
+  or
+- \<pr number>.md
+  or
+- \<random number>.md if none of other apply
+
+The content of the file should look like this:
+
+```
+### <type of change>
+
+- description of the change in one or max two sentences (#<issue> or !<pr>)
+```
+
+< type of change > can be one of:
+
+- **Added** for new features.
+- **Changed**: for changes in existing functionality.
+- **Deprecated**: for soon-to-be removed features.
+- **Removed**: for now removed features.
+- **Fixed**: for any bug fixes.
+- **Security**: in case of vulnerabilities.
+
+## Example
+
+```
+### Fixed
+
+- improve userdashboard filter performance (#2449)
+```
+
+## Create release changelog
+
+To create the changelog for a release you can either copy the content
+of all the changelog files into CHANGELOG.md manually or use the
+`parse_changelogs.py` in this folder by running it here:
+`./parse_changelogs.py`.

changelog/_0001.md

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+### Added
+
+- add a CHANGELOG.md and changelog/ folder

changelog/parse_changelogs.py

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+#!/bin/python3
+
+import logging
+import os
+import re
+from collections import OrderedDict
+
+logger = logging.getLogger(__name__)
+
+
+def combine_sections_in_folder(folder_path):
+    """Parser for changelog files following the https://keepachangelog.com
+    format.
+    """
+    allowed_section_headers = [
+        "Added",
+        "Changed",
+        "Deprecated",
+        "Removed",
+        "Fixed",
+        "Security",
+    ]
+    sections = OrderedDict()
+
+    for filename in os.listdir(folder_path):
+        if filename.endswith(".md") and filename != "README.md":
+            filepath = os.path.join(folder_path, filename)
+            with open(filepath, "r") as file:
+                current_section = None
+                for line in file:
+                    # find all headings starting with # (they should always
+                    # start with ### but we seem to sometimes use # or ##)
+                    match = re.match(r"^#+ (.*)", line)
+                    if match:
+                        section_header = match.group(1).strip().capitalize()
+                        if section_header not in allowed_section_headers:
+                            logger.warning(
+                                f"warning: section_header {section_header} "
+                                f"in file {filename} is invalid, "
+                                "see https://keepachangelog.com for a list of "
+                                "allowed types."
+                            )
+                        current_section = sections.get(section_header, [])
+                    elif current_section is not None and line.strip():
+                        current_section.append(line)
+                        sections[section_header] = current_section
+
+    combined_md = ""
+    for section_header, lines in sections.items():
+        combined_md += "### " + section_header + "\n\n"
+        combined_md += "".join(lines) + "\n"
+
+    return combined_md
+
+
+if __name__ == "__main__":
+    folder_path = "."
+    combined_md = combine_sections_in_folder(folder_path)
+    print(combined_md)