Add endpoints for browsed links and external sources

[Josh-XT]

Add functions for the following endpoints:

• GET /api/agent/{agent_name}/browsed_links
• DELETE /api/agent/{agent_name}/browsed_links
• GET /api/agent/{agent_name}/memory/external_sources
• DELETE /api/agent/{agent_name}/memory/external_source

See Josh-XT/AGiXT#1184 for more details.