use '*' prefix for config option values instead of escape sequences
The custom Sphinx extension that generates documentation from config.cc
help messages has issues with C++ escape sequences. For example,
"\tall: All traffic" renders incorrectly as "tall: All traffic" in HTML
output.
Instead of using escape sequences, switch to bullet-point style with '*'
prefix which works better in both CLI and HTML rendering. This matches
our existing documentation style for available option values in other
configs.
Note: This change puts type/default/liveness info in the same bullet
list as option values. This limitation affects other similar config
options and will need to be addressed comprehensively in a future
change.
Refs scylladb/scylladb#22423
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>