Update IS-5.3.0 official documentation with JDK 8 in order to work with FIDO2 and get cxf3 fixes

[Kanapriya]

Description:

Related to: wso2/product-is#7668

Need to update IS 5.3.0 documentation [1] with the following information:
After the timestamp 1567081633573, In-order to work with Fido2 and to get the CXF3 runtime feature for IS-5.3.0, it's mandatory to use JDK 1.8

[1] https://docs.wso2.com/display/IS530/Installation+Prerequisites

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