* cron: skip delivery for HEARTBEAT_OK responses
When an isolated cron job has deliver:true, skip message delivery if the
response is just HEARTBEAT_OK (or contains HEARTBEAT_OK at edges with
short remaining content <= 30 chars). This allows cron jobs to silently
ack when nothing to report but still deliver actual content when there
is something meaningful to say.
Media is still delivered even if text is HEARTBEAT_OK, since the
presence of media indicates there's something to share.
* fix(heartbeat): make ack padding configurable
* chore(deps): update to latest
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Co-authored-by: Josh Lehman <josh@martian.engineering>
