Add alter table JSON API

- Add POST /<database>/<table>/-/alter with Pydantic validation and dry-run support.
- Support add, rename, alter, drop, primary-key and reorder operations, including allow-listed default expressions.
- Document the endpoint and cover schema changes, validation, permissions, events and dry runs.

Refs #2788

pyproject.toml

@@ -39,6 +39,7 @@ dependencies = [
     "asyncinject>=0.7",
     "setuptools",
     "pip",
+    "pydantic>=2",
 ]
 
 [project.urls]