CLI: change binary name to svix-cli (#1597)

This is to help clarify what the binary actually is among the rest of
the svix tooling in the repo.

Looking forward, this will also help to keep the naming scheme
consistent between the binary, the package name, and the updater while
handling distribution via `dist` (pending PR:
#1593)

svix-cli/Cargo.toml

@@ -8,10 +8,6 @@ license = "MIT"
 keywords = ["svix", "webhooks", "diahook"]
 categories = ["development-tools", "asynchronous", "network-programming", "web-programming"]
 
-[[bin]]
-name = "svix"
-path = "src/main.rs"
-
 [dependencies]
 anyhow = "1.0.94"
 base64 = "0.22.1"