Improve data distribution: solve LP task on failure domains instead of individual OSDs

This greatly speeds up PG placement and makes it more uniform both because the LP task
becomes simpler and because the distribution of individual OSDs is optimised manually

mon/lp_optimizer/lp_optimizer.js

@@ -98,6 +98,7 @@ async function optimize_initial({ osd_weights, combinator, pg_count, pg_size = 3
         score: lp_result.score,
         weights: lp_result.vars,
         int_pgs,
+        pg_effsize,
         space: eff * pg_effsize,
         total_space: total_weight,
     };
@@ -409,6 +410,7 @@ async function optimize_change({ prev_pgs: prev_int_pgs, osd_weights, combinator
         int_pgs: new_pgs,
         differs,
         osd_differs,
+        pg_effsize,
         space: pg_effsize * pg_list_space_efficiency(new_pgs, osd_weights, pg_minsize, parity_space),
         total_space: total_weight,
     };