Dedup exact same selectors while keep original precedence

[Eskibear]

Dedup same selectors can save requests. And we should ensure the precedence of originally passed selectors unchanged.

selectors: [ 
            { keyFilter: "app.*", labelFilter: "dev" },
            { keyFilter: "app.*", labelFilter: "production" },
            { keyFilter: "app.*", labelFilter: "dev" },
] 

Without dedup, it's clear that the last "app.* + dev" wins. After dedup, we should keep the same precedence, and in this case let "app.* + dev" win.

Originally posted by Yan Zhang (@Eskibear) in #22 (comment)