Set new default index, Simplify the prompt template

[bmquinn]

• Sets the default to the better "DCWork" index
• Swaps the long default prompt for one that @mbklein was testing locally. It not only seems to make better responses in my development environment, but has a much smaller token count which lets us add more metadata and/or reduce the average token count per request. 🎉

[kdid]

@bmquinn Cool. Can you link this to an issue that describes the work, like we talked about yesterday? Also, for my benefit, an example in the PR about how to invoke with the new param options like a prompt template would be helpful. 🙏