opt: add settings to enable usage of histograms and multi-column stats

[jseldess]

PR: cockroachdb/cockroach#48105

From release notes:

Added two new session variables and corresponding cluster settings to control whether the optimizer uses histograms and multi-column statistics for cardinality estimation. The session variables are optimizer_use_histograms and optimizer_use_multicol_stats, with corresponding cluster settings sql.defaults.optimizer_use_histograms.enabled and sql.defaults.optimizer_use_multicol_stats.enabled. Both settings are enabled by default. [#48105][#48105] {% comment %}doc{% endcomment %}