Expose foreign key data to alter table UI

Include current foreign key metadata in the alter table page data and allow the foreign-key-targets endpoint to be read by actors with alter-table permission for a specific table.

Add API and HTML data tests for the new alter-table foreign key support.

tests/test_api_write.py

@@ -1252,6 +1252,17 @@ async def test_foreign_key_targets_permission_denied(ds_write):
     }
 
 
+@pytest.mark.asyncio
+async def test_foreign_key_targets_allowed_for_alter_table(ds_write):
+    token = write_token(ds_write, permissions=["at"])
+    response = await ds_write.client.get(
+        "/data/-/foreign-key-targets?table=docs",
+        headers=_headers(token),
+    )
+    assert response.status_code == 200, response.text
+    assert response.json()["ok"] is True
+
+
 @pytest.mark.asyncio
 async def test_alter_table_permission_denied(ds_write):
     token = write_token(ds_write, permissions=["ir"])