Update test setup to index test data after old indexing code removed

- Delete tests testing deprecated server side indexing flows
- Delete `Local(Plaintext|Org|Markdown|Pdf)Config' methods, files and
  references in tests
- Index test data via new helper method, `get_index_files'
  - It is modelled after the old `get_org_files' variants in main app
  - It passes the test data in required format to `configure_content'
    Allows maintaining the more realistic tests from before while
    using new indexing mechanism (rather than the deprecated server
    side indexing mechanism

tests/test_agents.py

@@ -15,7 +15,7 @@ from tests.helpers import ChatModelFactory
 def test_create_default_agent(default_user: KhojUser):
     ChatModelFactory()
 
-    agent = AgentAdapters.create_default_agent(default_user)
+    agent = AgentAdapters.create_default_agent()
     assert agent is not None
     assert agent.input_tools == []
     assert agent.output_modes == []