feat: add bot name customization and update greeting message

[aimanfazal]

Changes

• Added a bot_name field to user_memory to store the customized bot name.
• Set the default bot name to "Jacob".
• Updated the greeting message to use the configured bot name.
• Added support for updating the bot's name during a conversation through natural language commands (e.g., "set your name to", "change your name to", or "your name is").