Fix the typo in callout # 2 in step 3 of https://docs.openshift.com/container-platform/4.12/monitoring/configuring-the-monitoring-stack.html#configuring_remote_write_storage_configuring-the-monitoring-stack

Currently, it says "authentication using HTTP an Authorization request header"; it should be corrected to say "authentication using HTTP in an Authorization request header".

In addition, update "basic authentication" to "Basic authentication" to follow the new Supplementary style guide guidance.