postgresql: Add schema v4.6 with more indexes

Add PostgreSQL schema v4.6 adding more indexes to help Grafana
dashboards.

kcidb/db/postgresql/__init__.py

@@ -2,7 +2,7 @@
 
 import textwrap
 from kcidb.db.schematic import Driver as SchematicDriver
-from kcidb.db.postgresql.v04_05 import Schema as LatestSchema
+from kcidb.db.postgresql.v04_06 import Schema as LatestSchema
 
 
 class Driver(SchematicDriver):

kcidb/db/postgresql/v04_06.py

@@ -0,0 +1,41 @@
+"""Kernel CI report database - PostgreSQL schema v4.6"""
+
+from kcidb.misc import merge_dicts
+from kcidb.db.postgresql.schema import Index
+from .v04_05 import Schema as PreviousSchema
+
+
+# It's OK, pylint: disable=too-many-ancestors
+class Schema(PreviousSchema):
+    """PostgreSQL database schema v4.6"""
+
+    # The schema's version.
+    version = (4, 6)
+
+    # A map of index names and schemas
+    INDEXES = merge_dicts(PreviousSchema.INDEXES, dict(
+        checkouts_valid=Index("checkouts", ["valid"]),
+        builds_compiler=Index("builds", ["compiler"]),
+        builds_valid=Index("builds", ["valid"]),
+        tests_waived=Index("tests", ["waived"]),
+    ))
+
+    @classmethod
+    def _inherit(cls, conn):
+        """
+        Inerit the database data from the previous schema version (if any).
+
+        Args:
+            conn:   Connection to the database to inherit. The database must
+                    comply with the previous version of the schema.
+        """
+        assert isinstance(conn, cls.Connection)
+        with conn, conn.cursor() as cursor:
+            for index_name, index_schema in cls.INDEXES.items():
+                if index_name not in PreviousSchema.INDEXES:
+                    try:
+                        cursor.execute(index_schema.format_create(index_name))
+                    except Exception as exc:
+                        raise Exception(
+                            f"Failed creating index {index_name!r}"
+                        ) from exc