Added a new backend settings system

This can be used for saving runtime-configurable settings in the database.

spoolman/database/models.py

@@ -3,7 +3,7 @@
 from datetime import datetime
 from typing import Optional
 
-from sqlalchemy import ForeignKey, Integer, String
+from sqlalchemy import ForeignKey, Integer, String, Text
 from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column, relationship
 
 
@@ -58,3 +58,11 @@ class Spool(Base):
     lot_nr: Mapped[Optional[str]] = mapped_column(String(64))
     comment: Mapped[Optional[str]] = mapped_column(String(1024))
     archived: Mapped[Optional[bool]] = mapped_column()
+
+
+class Setting(Base):
+    __tablename__ = "setting"
+
+    key: Mapped[str] = mapped_column(String(64), primary_key=True, index=True)
+    value: Mapped[str] = mapped_column(Text())
+    last_updated: Mapped[datetime] = mapped_column()