Don't always encode forward slashes as %2F in query parameters

[scnerd]

#2723 Transitions to encoding "/" as "%2F" in the query; the argument is that this is "more correct" and more inline with browsers' default behavior.

The problem is that some API's simply reject this; for them, the two encodings are not identical. A comment on #2721 remarks that the OpenAI API expects actual slashes. I'm dealing with a private backend (that I don't control) that likewise expects actual slashes.

This new behavior should be possible to opt out of.

[thetanz-geoff]

@scnerd: This is raised in discussions (per the rules: "Please only raise an issue if you've been advised to do so after discussion.") here:
#2856
#2863

Suggest you keep an eye on all 3 threads for a response, and downgrade to 0.24.1 in the interim.

[zanieb]

Closing in favor of the existing discussions for now.