What is an API client registry? <span class="bsf-rt-reading-time"><span class="bsf-rt-display-label" prefix="Reading Time"></span> <span class="bsf-rt-display-time" reading_time="3"></span> <span class="bsf-rt-display-postfix" postfix="mins"></span></span><!-- .bsf-rt-reading-time -->