RFC - Rename DuckDuckGoSearchTool to use -Run postfix to be consistent with other classes.

[skcoirz]

I found most other search classes are using -Run postfix except DuckDuckGo. It might be good to keep them consistent. (screenshot below)

• Updated all places (using big search and following the original PR https://github.com/hwchase17/langchain/pull/3206)
• lint and text passed on local
• Retested jupyter example. (btw, for anyone who’s not familiar jupyter + virtual env. Here are the steps to run Jupyter in a selected Virtual Env) — screenshot below.

reference: https://www.geeksforgeeks.org/using-jupyter-notebook-in-virtual-environment/#
- Activate the Virtual Env
- ipython kernel install --user —name=<your virtual env name>
- In Jupyter, change Kernel. (in menu)

Please let me know if this makes sense. I’m new here and still ramping up. I can remove it if this doesn’t help. Thanks so much!

reference 1 - Most search classes are using -Run postfix.

reference 2 - Jupyter example is also verified.