Allow management operations like deleting files

This introduces the X-Token header field in the response of newly
uploaded files as a simple way for users to manage their own files.

It does not need to be particularly secure.

migrations/versions/0659d7b9eea8_.py

@@ -0,0 +1,26 @@
+"""add file management token
+
+Revision ID: 0659d7b9eea8
+Revises: 939a08e1d6e5
+Create Date: 2022-11-30 01:06:53.362973
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '0659d7b9eea8'
+down_revision = '939a08e1d6e5'
+
+from alembic import op
+import sqlalchemy as sa
+
+
+def upgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.add_column('file', sa.Column('mgmt_token', sa.String(), nullable=True))
+    # ### end Alembic commands ###
+
+
+def downgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_column('file', 'mgmt_token')
+    # ### end Alembic commands ###