[book] Update documentation for new repoapi Quite a few things change in 3.19: - repoapi instead of dbapi - ClientConnection / Connection / Session rework - web authentication process - test APIs Closes #3638793

option_group_changed('port', 'main', 'web')
option_group_changed('query-log-file', 'main', 'web')
option_group_changed('profile', 'main', 'web')
option_group_changed('max-post-length', 'main', 'web')