Fix blocking send in online Histo sender

• Fixes the sometime 40s-1min long waits when sending histos for CA or event builder (probable cause for jumps in TS count in Grafana)
• Should also fix the blocking wait at startup if no histogram server available if I believe https://libzmq.readthedocs.io/en/latest/zmq_msg_send.html

Redmine Refs #3290 #3289

For info: ping @fweig @j.decuveland

added BugFix Online QA labels

assigned to @p.-a.loizeau

Set to auto-merge as tested locally

enabled an automatic merge when the pipeline for e3a7301b succeeds

Dear @d.smith, @fweig,

you have been identified as code owner of at least one file which was changed with this merge request.

Please check the changes and approve them or request changes.

added CodeOwners label

merged