A config option value is reported as 'text' type and contains
a string as it would looks like in json config.
The table is UPDATE-able. Only the 'value' columnt can be set
and the value accepted must be string. It will be converted into
the option type automatically, however in current implementation
is't not 100% precise -- conversion is lexicographical cast which
only works for simple types. However, liveupdate-able values are
only of those types, so it works in supported cases.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>