database: added keys migration, get/insert, insert keys at launch if none are present

crates/database/migrations/20230312153840_keys.down.sql

@@ -0,0 +1 @@
+drop table if exists keys;

crates/database/migrations/20230312153840_keys.up.sql

@@ -0,0 +1,8 @@
+create table if not exists keys
+(
+    id          TEXT not null primary key,
+    created_at  TEXT not null default CURRENT_TIMESTAMP,
+    revoked_at  TEXT,
+    private_der BLOB not null,
+    public_der  BLOB not null
+);