cli does handle proxy environment variables with trailing slash

[romain-grecourt]

If the proxy set in the environment contains non digit characters after the port, the bad characters are included.
E.g. https_proxy=com.acme:80/

The code in io.helidon.build.common.Proxies should be improved to be as robust and flexible as possible.
I.e. If an existing environment works with other tools, it should work with the Helidon CLI.

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E.g.

export https_proxy=com.acme:80/
helidon --debug init --reset

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• Update io.helidon.build.common.Proxies to be unit testable (extract the parsing logic in package private static methods)
• Take some inspiration from Helidon WebClient (discard socks proxies)
• Find the standard or pseudo standard, add references to them in the code