Complete implementation of modern http client for ECF

Recall that ECF provides two transport implementations as used by p2, but the newer one, based on built-in Java support, is not fully functional with respect to more complex network configurations, so we've needed to disable it. ECF #76 covers this issue.

• task name and Gitlab Issue id,
  • Complete implementation of modern http client for ECF
• time estimate, if possible,
  • a couple of weeks to setup test infrastructure to be able to test the various supported network configurations in addition to the 1-3 weeks it may take to resolve this issue
• expected deliverable(s)/outcome(s),
  • PRs for the ECF project
  • PR for the Eclipse Platform project to remove old version of http client if possible
    • see for example the feature.xml which refers to both versions
  • PR for the Eclipse Packaging Project (EPP) to remove the exclusion of the Java provider
    • see for example this touchpoint
  • Updates to New and Noteworthy / Changelogs as needed
• identify any dependencies on external resources including Eclipse IT infrastructure updates,
  • The ongoing challenge with the http client is supporting complex proxy configurations. Having a test setup that supports this may require some support from the Eclipse IT team
• means of demonstration and/or verification of completion.
  • ECF use by p2 can install and check for updates using the newer http client.