Don't throw unchecked exceptions when creating requests for builders

[StefanBratanov]

PR Description

All exceptions are currently handled in the OkHttp callback onFailure method.

This PR makes sure no unchecked exception (different from expected IOException) is thrown in RequestBody.writeTo method. If such is thrown, then an exception will be thrown in a background thread, which will trigger TekuDefaultExceptionHandler to print a scary log message.

Fixed Issue(s)

fixes #6109

Documentation

• I thought about documentation and added the doc-change-required label to this PR if updates are required.

Changelog

• I thought about adding a changelog entry, and added one if I deemed necessary.

[tbenr]

LGTM.
Even if its only in test code, pinging @ajsutton for an approval on adding awaitility dependency.

[StefanBratanov]

LGTM. Even if its only in test code, pinging @ajsutton for an approval on adding awaitility dependency.

Cool, I used it to get the catchUncaughtExceptions functionality, which fails the test if exceptions are caught in background threads. Otherwise, needed to create a separate thread and attach a test handler to it.