Gitpodify - Add support to launch Open UI in Gitpod

[davemecha]

With this PR I want to suggest adding Gitpod support. Gitpod is an online dev environment and browser based IDE (similar to Github Codespaces with some additional features).

The PR contains the following changes:

• I added a simple .gitpod.yml that defines how the Gitpod container should be started.
  • On workspace initialization it sets up an Open UI python virtual environment.
  • Installs backend dependencies with pip as described in the README.
  • It starts the Open UI backend, ready to use if OPENAI_API_KEY is provided.
• I added a Gitpod section in the README with an "Open in Gitpod" button.

To use Gitpod a user needs a (free) Gitpod account. To use the Open AI API, the OPENAI_API_KEY must be provided as an environment variable as described in the README.

I did not set up Ollama by default, since the default Gitpod containers are not too powerful. I didn't try it. Do you think this should be added or should we provide some simple script to automate the setup in Gitpod? We could also set it up but not launch it. So it's ready to go.

What do you think about this PR? What should be improved?

[vanpelt]

Cool!