Make account shrink configurable #17544 (#17778)

1. Added both options for measuring space usage using total accounts usage and for individual store shrink ratio using an enum. Validator CLI options: --accounts-shrink-optimize-total-space and --accounts-shrink-ratio
2. Added code for selecting candidates based on total usage in a separate function select_candidates_by_total_usage
3. Added unit tests for the new functions added
4. The default implementations is kept at 0.8 shrink ratio with --accounts-shrink-optimize-total-space set to true

Fixes #17544

core/tests/snapshots.rs

@@ -106,6 +106,7 @@ mod tests {
                 None,
                 AccountSecondaryIndexes::default(),
                 false,
+                accounts_db::AccountShrinkThreshold::default(),
             );
             bank0.freeze();
             let mut bank_forks = BankForks::new(bank0);
@@ -165,6 +166,7 @@ mod tests {
             AccountSecondaryIndexes::default(),
             false,
             None,
+            accounts_db::AccountShrinkThreshold::default(),
         )
         .unwrap();