Replace .netrc with uv environment variables (#1541)

This commit replaces .netrc with uv environment variables for installing
tools from private repositories. To store credentials, I created a new
and reusable settings file for the CLI in
`$HOME/.config/crewai/settings.json`.

The issue with .netrc files is that they are applied system-wide and are
scoped by hostname, meaning we can't differentiate tool repositories
requests from regular requests to CrewAI's API.

tests/cli/tools/test_main.py

@@ -82,6 +82,7 @@ def test_install_success(mock_get, mock_subprocess_run):
         capture_output=False,
         text=True,
         check=True,
+        env=unittest.mock.ANY
     )
 
     assert "Succesfully installed sample-tool" in output