Implement filtering by severity and release channel

This also involves a refactoring of the way reports are encoded: rather than using plaintext error messages, use readable codes and structured metadata for errors and updates to make them easier to process.

️🧪 Test rendering here: https://infrastructure.pages.apertis.org/-/dashboard/-/jobs/1376068/artifacts/public/index.html

Task: https://phabricator.apertis.org/T7889

bin/classes.py

 import dataclasses
+import enum
 import typing
 
 import debian.debian_support
@@ -15,6 +16,39 @@ RENAMED = {
 }
 
 
+class Report(enum.Enum):
+    def _generate_next_value_(name, start, count, last_values):
+        return name.lower().replace("_", "-")
+
+    APT_PACKAGE_BINARIES_AMBIGUOUS = enum.auto()
+    APT_PACKAGE_BINARIES_MISSING = enum.auto()
+    APT_PACKAGE_MISSING = enum.auto()
+    APT_PACKAGE_MISSING_BUT_ON_OBS = enum.auto()
+    APT_PACKAGE_SOURCE_AMBIGUOUS = enum.auto()
+    APT_PACKAGE_SOURCE_MISSING = enum.auto()
+    APT_PACKAGE_SOURCE_VERSION_MISMATCH_BINARIES = enum.auto()
+    APT_PACKAGE_VERSION_MISMATCH_OBS = enum.auto()
+    GIT_BRANCH_COMPONENT_MISSING = enum.auto()
+    GIT_BRANCH_FOLDED_BUT_NOT_REMOVED = enum.auto()
+    GIT_BRANCH_HAS_AMBIGUOUS_TAGS = enum.auto()
+    GIT_BRANCH_LICENSING_REPORT_MISSING = enum.auto()
+    GIT_BRANCH_MISSING_BUT_ON_OBS = enum.auto()
+    GIT_BRANCH_NOT_POINTING_TO_TAGGED_COMMIT = enum.auto()
+    GIT_BRANCH_PIPELINE_FAILED = enum.auto()
+    GIT_CHANNEL_LAGGING = enum.auto()
+    GIT_PROJECT_MISSING = enum.auto()
+    GIT_UPSTREAM_BRANCH_DROPPED = enum.auto()
+    GIT_UPSTREAM_BRANCH_NOT_MERGED = enum.auto()
+    OBS_PACKAGE_AMBIGUOUS = enum.auto()
+    OBS_PACKAGE_BUILD_FAILED = enum.auto()
+    OBS_PACKAGE_MISSING_BUT_IN_GIT = enum.auto()
+    OBS_PACKAGE_MISSING_BUT_ON_APT = enum.auto()
+    OBS_PACKAGE_MISSING_BUT_PUBLISHED = enum.auto()
+    OBS_PACKAGE_VERSION_MISMATCH = enum.auto()
+    UPDATE_AVAILABLE = enum.auto()
+    UPDATE_AVAILABLE_MAINLINE = enum.auto()
+
+
 @dataclasses.dataclass
 class UpstreamPackage:
     name: str