[Java][Spring] fix wrong values with enum variables in path parameters which generated allowableValues with double quote

Created by: yangguangxiadeyun

Hi team and @jeff9finger @nmuesch @lwlee2608 , this PR is to fix wrong values with enum variables in path parameters which generated allowableValues with double quote(#6762 (closed)) According to javadoc swagger-annotations ApiParam, allowableValues sets a list of values, provide a comma-separated list. For example: first, second, third. If using double quote, the URL path would become something like http://example.com/foo/"bar" while we're expecting http://example.com/foo/bar. Thus I think we should not use double quote for each value when it's used in path variable.

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