Clarify path param naming (#32969)

In history (from some legacy frameworks), both `:name` and `name` are
supported as path path name, `:name` is an alias to `name`.

To make code consistent, now we should only use `name` but not `:name`.

Also added panic check in related functions to make sure the name won't
be abused in case some downstreams still use them.

routers/api/v1/repo/notes.go

@@ -52,7 +52,7 @@ func GetNote(ctx *context.APIContext) {
 	//   "404":
 	//     "$ref": "#/responses/notFound"
 
-	sha := ctx.PathParam(":sha")
+	sha := ctx.PathParam("sha")
 	if !git.IsValidRefPattern(sha) {
 		ctx.Error(http.StatusUnprocessableEntity, "no valid ref or sha", fmt.Sprintf("no valid ref or sha: %s", sha))
 		return