Improve istioversion package by adding a way to get latest patch version for each minor version

[fjglira]

Currently, the istioversion package parses the versions.yaml file and get information about the versions from there. To be able to properly filter the latest patch version for each minor version we need to improve the func and give the user the possibility to select for example latest patch for each minor version

[fjglira]

The package already had a Map with all the version, I'm adding a func in the e2e util to get latest patch for each minor and used in the test