Add duckdb_optimizers function

[Mytherin]

D FROM duckdb_optimizers();
┌────────────────────────────┐
│            name            │
│          varchar           │
├────────────────────────────┤
│ expression_rewriter        │
│ filter_pullup              │
│ filter_pushdown            │
│ regex_range                │
│ in_clause                  │
│ join_order                 │
│ deliminator                │
│ unnest_rewriter            │
│ unused_columns             │
│ statistics_propagation     │
│ common_subexpressions      │
│ common_aggregate           │
│ column_lifetime            │
│ top_n                      │
│ compressed_materialization │
│ duplicate_groups           │
│ reorder_filter             │
│ extension                  │
├────────────────────────────┤
│          18 rows           │
└────────────────────────────┘

This is useful when combined with PRAGMA disabled_optimizers

[Mytherin]

CC @szarnyasg