add support for Adoptium Eclipse Temurin Java

[e-kotov]

Add support for a new Java distribution, specifically for Adoptium Eclipse Temurin.

The parametrized urls for Amazon Corretto Java, are currently hardcoded in inst/extdata/java_urls.json.

I don't exactly know what is the URL scheme for Adoptium Eclipse Temurin Java. It may be easy to hardcode similar URLs in the inst/extdata/java_urls.json, but perhaps a new mechanism for fetching some kind of xml or rss is needed to implement this support.

Warning, adding the support for another Java distribution may require changes to several package functions, so please, whomever takes on this issue, expect to spend perhaps more than 1-2 hours on it.

P.S. This would be the first step to solving the issue #18 .