Do not store uv cache, uv to use venv interpreter

[ogajduse]

Problem Statement

1. uv cache bloats the image and also causes issues in the downstream image build
2. during the image build, in the RUN step, the shell environment is not sourced, the python environment in $APP_ROOT is not activated and therefore VIRTUAL_ENV env variable is not defined. That causes uv not to discover the venv interpreter and it creates its env in .venv and installs robottelo in it.

Solution

1. as the upstream fedora/python-312 image forces pip to not create the cache, we should mimic it for uv too
   • set UV_NO_CACHE=1
2. Tell uv to use Python from the existing virtual env
   • set UV_PYTHON="${APP_ROOT}/bin/python3"