Add new declare method (#461)

For manually declare (or overwrite) missing or erroneous versions.

src/declare.py

@@ -0,0 +1,16 @@
+from datetime import datetime
+
+from common.releasedata import ProductData, config_from_argv
+
+"""Manually declare missing or erroneous versions."""
+
+config = config_from_argv()
+with ProductData(config.product) as product_data:
+    for version in config.data.get("versions", []):
+        product_data.declare_version(version['name'], version['date'])
+
+    releases: list[dict[str, str | bool | datetime]] = config.data.get("releases", [])
+    for release in releases:
+        release_data = product_data.get_release(release.pop("name"))
+        for key, value in release.items():
+            release_data.set_field(key, value)