doc/rados: Fix minor issues, improvements in health-checks.rst (5 of x)

doc/rados: Fix minor issues, improvements in health-checks.rst (5 of x)

Remove spaces at the end of lines.

Use confval instead of simple inline literal text for config values.

Use double backticks consistently for literals.

Attempt minor language improvements.

Use "Monitor", "Manager" consistently.

Add a link to stretch mode doc in relevant sections.

Use a privileged prompt for CLI command examples requiring privileges.

Linkify mentions of other sections in the document.

Signed-off-by: Ville Ojamo <14869000+bluikko@users.noreply.github.com>