Switch to Java 11 HttpClient

[rymsha]

Currently lib-httpclient uses OkHttpClient. There are a few problems with it:

• OkHttpClient written in Kotlin and entire Kotlin lib bundled into application jar. App jar becomes quite big
• During build time OSGi looks for annotations in all the classes, including Kotlin lib classes. It adds a few seconds to application build time
• The way OKHttpclient is used (and it is dictated by current lib-http-client) API , entire HttpcCient instance with a new thread pool is created

Is we switch to Java 11 HttpClient we don't need to bundle Kotlin lib, nor any additional classes - as they are part of JDK. It will lead to faster builds and smaller artifacts.

It is a "major version" change and we can take a chance to change the API so it does not require us to create a new connection every time. (connectTimeout, certificates and clientCertificate are connection related)

[sigdestad]

+1 on this. 30MB 30second build time sux

[rymsha]

• connection pool
• expires for cookies
• response body offload to file