fix: Use the Enum's value for the dictionary key when responding to an admin request for experimental features

[realtyem]

While exploring bring up of using orjson, exposed an interesting flaw. The stdlib json encoder seems to be ok with coercing a str from an Enum(specifically, a Class[str, Enum]). The orjson encoder does not like that this is a class and not a proper str per spec. Using the .value of the enum as the key for the dict produced while answering a GET admin request for experimental features seems to fix this.

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