If you want to permanently enable soft wrap for certain file extensions, it can be configured in Settings > Editor> General. Under the title Soft Wraps, add your required file extension.

The settings can also be accessed by right-click on the line-numbers and selecting Configure Soft Wraps as explained here. Also shown here.

PS: I know it is not what is asked in the question, but this was the first google result when I searched for configuring soft wraps. So, I added the answer here in case anybody else comes looking up for the same.