Remove the signing keys DB table and API (#2252)

It is completely unused now.

Author: jhrozek

database/migrations/000015_remove_signing_keys.down.sql

@@ -0,0 +1,25 @@
+-- Copyright 2024 Stacklok, Inc
+--
+-- Licensed under the Apache License, Version 2.0 (the "License");
+-- you may not use this file except in compliance with the License.
+-- You may obtain a copy of the License at
+--
+--      http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing, software
+-- distributed under the License is distributed on an "AS IS" BASIS,
+-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+-- See the License for the specific language governing permissions and
+-- limitations under the License.
+
+-- signing_keys table
+CREATE TABLE signing_keys (
+                              id SERIAL PRIMARY KEY,
+                              project_id UUID NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
+                              private_key TEXT NOT NULL,
+                              public_key TEXT NOT NULL,
+                              passphrase TEXT NOT NULL,
+                              key_identifier TEXT NOT NULL,
+                              created_at TIMESTAMP NOT NULL DEFAULT NOW(),
+                              updated_at TIMESTAMP NOT NULL DEFAULT NOW()
+);

database/migrations/000015_remove_signing_keys.up.sql

@@ -0,0 +1,15 @@
+-- Copyright 2024 Stacklok, Inc
+--
+-- Licensed under the Apache License, Version 2.0 (the "License");
+-- you may not use this file except in compliance with the License.
+-- You may obtain a copy of the License at
+--
+--      http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing, software
+-- distributed under the License is distributed on an "AS IS" BASIS,
+-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+-- See the License for the specific language governing permissions and
+-- limitations under the License.
+
+DROP TABLE IF EXISTS signing_keys;