Database log message is truncated at 56 characters and not configurable

Description of the need

The database log report at admin/reports/dblog limits the log message length to 56 characters before truncation. This is inadequate for my use case and window size, and requires much clicking of links to see log details.

It was possible in Drupal 7 to alter the log display by overriding the dblog_message theme function, however that capability was removed in https://github.com/backdrop/backdrop/pull/629.

Proposed solution

Provide a numeric setting for log message line length on the admin/config/development/logging page.

Draft of feature description for Press Release (1 paragraph at most)

Backdrop now includes a setting to limit dblog message length before truncation.