Status monitor message override

[jskupsik]

Hoist P/R Checklist

Pull request authors: Review and check off the below. Items that do not apply can also be
checked off to indicate they have been considered. If unclear if a step is relevant, please leave
unchecked and note in comments.

• Caught up with develop branch as of last change.
• Added CHANGELOG entry, or determined not required.
• Reviewed for breaking changes, added breaking-change label + CHANGELOG if so.
• Updated doc comments / prop-types, or determined not required.
• Reviewed and tested on Mobile, or determined not required.
• Created Toolbox branch / PR, or determined not required.

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Pull request reviewers: when merging this P/R, please consider using a squash commit to
collapse multiple intermediate commits into a single commit representing the overall feature
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single commit should be rebased when possible.

[jskupsik]

Issue: xh/hoist-core#268
Toolbox PR: xh/toolbox#603
hoist-core PR: xh/hoist-core#269

Backwards and forwards compatible:
Old hoist-core + new hoist-react = appears identical to old behavior, the non-success message overrides any user-provided
New hoist-core + old hoist-react = the messages on the monitor card are displayed on the same line, rather than a newline