chore: add llamaindex chat agent sample

[GabrielVasilescu04]

Description

Add a chat-agent sample for the llamaindex integration

Development Packages

uipath-llamaindex

[project]
dependencies = [
  # Exact version:
  "uipath-llamaindex==0.5.7.dev1001950929",

  # Any version from PR
  "uipath-llamaindex>=0.5.7.dev1001950000,<0.5.7.dev1001960000"
]

[[tool.uv.index]]
name = "testpypi"
url = "https://test.pypi.org/simple/"
publish-url = "https://test.pypi.org/legacy/"
explicit = true

[tool.uv.sources]
uipath-llamaindex = { index = "testpypi" }