ROUTE53: Add weighted routing and health check support

[Crazu]

Adds R53_WEIGHT(weight, set_identifier) and R53_HEALTH_CHECK_ID(id) record modifiers for Route 53 weighted routing policies.

    A("www", "1.2.3.4",
        R53_WEIGHT(70, "primary"),
        R53_HEALTH_CHECK_ID("12345678-1234-1234-1234-123456789000")
    ),
    A("www", "5.6.7.8",
        R53_WEIGHT(30, "secondary"),
        R53_HEALTH_CHECK_ID("12345678-1234-1234-1234-123456789001")
    )

The R53_WEIGHT_HEALTH_CHECK integration test is problematic because it references non existent AWS health check IDs. Route 53 will reject these API calls because it validates that all health check IDs refer to existing resources created externally.

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