go: use PathEscape instead of QueryEscape to escape path params

Created by: bendrucker

This PR uses url.PathEscape instead of url.QueryEscape to escape path parameters. PathEscape performs what would typically be called "URL encoding" with percents. PathEscape replaces spaces with pluses among other encoding that's suitable for query parameters.

package main

import (
	"fmt"
	"net/url"
)

func main() {
	input := "foo bar"
	fmt.Println("QueryEscape:", url.QueryEscape(input))
	fmt.Println("PathEscape:", url.PathEscape(input))
}

QueryEscape: foo+bar
PathEscape: foo%20bar

https://play.golang.org/p/3gWzjBhMR9C

Escaping was originally added in #3643.

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