[rb] Feat 15905/deprecate ftp proxy (#15926)

* add deprecation warn for ftp proxy type

* [proxy] Replace deprecation warning for FTP proxy support with logger method

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Co-authored-by: Augustin Gottlieb <[email protected]>

Author: iampopovich

rb/lib/selenium/webdriver/common/proxy.rb

@@ -77,6 +77,7 @@ def ==(other)
       alias eql? ==
 
       def ftp=(value)
+        WebDriver.logger.deprecate('FTP proxy support', nil, id: :ftp_proxy)
         self.type = :manual
         @ftp = value
       end