Remove manual mapping in FromStr implementation for StorySelector (#3018)

This PR removes the need for writing manual mappings in the `FromStr`
implementation for the `StorySelector` enum used in the storybook CLI.

We are now using the
[`EnumString`](https://docs.rs/strum/0.25.0/strum/derive.EnumString.html)
trait from `strum` to automatically derive snake_cased names for the
enums.

This will cut down on some of the manual work needed to wire up more
stories to the storybook.

Release Notes:

- N/A

crates/storybook/Cargo.toml

@@ -17,6 +17,7 @@ rust-embed.workspace = true
 serde.workspace = true
 settings = { path = "../settings" }
 simplelog = "0.9"
+strum = { version = "0.25.0", features = ["derive"] }
 theme = { path = "../theme" }
 ui = { path = "../ui" }
 util = { path = "../util" }