Improve LLM error messages

[agg23]

In situations where communication with the LLM fails, the OpenAI plugin should communicate some information about what failed. For example, if an invalid API URL is provided, the LLM currently speaks "EMPTY RESPONSE", which is useless.

09:19:46.128  6395-6489  HttpClient                com.penumbraos.plugins.openai        W  Creating flow for: http://url/chat/completions
09:19:46.128  6395-6489  HttpClient                com.penumbraos.plugins.openai        W  Current pending requests: 0
09:19:46.131  6395-6490  HttpClient                com.penumbraos.plugins.openai        W  Started HTTP request: http://url/chat/completions
09:19:46.132  6395-6490  HttpClient                com.penumbraos.plugins.openai        W  Generated request ID: 3f0722de-c23f-4a7f-b0dd-b4b8d7c2e70e
09:19:46.132  6395-6490  HttpClient                com.penumbraos.plugins.openai        W  Added request to pending map, size now: 1
09:19:46.132  6395-6490  HttpClient                com.penumbraos.plugins.openai        W  Making HTTP request: http://url/chat/completions
09:19:46.135  7504-7546  HttpProvider              app_process                          W  Making HTTP request: http://url/chat/completions
09:19:46.215  7504-7914  CustomDnsResolver         app_process                          E  Failed to resolve hostname url
09:19:46.222  6395-6489  HttpClient                com.penumbraos.plugins.openai        W  Finished iterating over channel responses
09:19:46.222  6395-6489  HttpClient                com.penumbraos.plugins.openai        W  Finished making HTTP request: http://url/chat/completions
09:19:46.224  6309-7905  CursorWindowStats         com.penumbraos.mabl.pin              I  Created a new Cursor. # Open Cursors=1 (# cursors opened by this proc=1)
09:19:46.225  6309-7905  SQLiteTime                com.penumbraos.mabl.pin              V  /data/user/0/com.penumbraos.mabl.pin/databases/app_database: "SELECT * FROM conversation_messages WHERE conversationId = ? ORDER BY timestamp ASC" took 0.000 ms
09:19:46.225  6309-7905  SQLiteCursor              com.penumbraos.mabl.pin              D  received count(*) from native_fill_window: 1
09:19:46.244  6395-6490  OpenAiLlmService          com.penumbraos.plugins.openai        W  LLM response received: "", 
09:19:46.246  6309-7910  InteractionFlowManager    com.penumbraos.mabl.pin              D  LLM complete response: EMPTY RESPONSE