pindexer: dex-explorer: implement low high in summary (#4931)

## Describe your changes

Closes #4929.

This was surprisingly simple, we were already doing an aggregate
calculation over the window (summing values) so this was just a matter
of adding a low and a high.

To test, index against main and check that nothing else has changed
besides the addition of two new fields.

## Checklist before requesting a review

- [x] I have added guiding text to explain how a reviewer should test
these changes.

- [x] If this code contains consensus-breaking changes, I have added the
"consensus-breaking" label. Otherwise, I declare my belief that there
are not consensus-breaking changes, for the following reason:

  > indexing

crates/bin/pindexer/src/dex_ex/mod.rs

@@ -443,7 +443,9 @@ mod summary {
             SELECT
                 COALESCE(SUM(direct_volume), 0.0) AS direct_volume_over_window,
                 COALESCE(SUM(swap_volume), 0.0) AS swap_volume_over_window,
-                COALESCE(SUM(trades), 0.0) AS trades_over_window
+                COALESCE(SUM(trades), 0.0) AS trades_over_window,
+                COALESCE(MIN(price), 0.0) AS low,
+                COALESCE(MAX(price), 0.0) AS high
             FROM snapshots
             WHERE time <= $3
             AND time >= $4
@@ -452,6 +454,7 @@ mod summary {
         SELECT 
             $1, $2, $5,
             price, price_then,
+            low, high,
             liquidity, liquidity_then,
             direct_volume_over_window,
             swap_volume_over_window,

crates/bin/pindexer/src/dex_ex/schema.sql

@@ -49,6 +49,8 @@ CREATE TABLE IF NOT EXISTS dex_ex_pairs_summary (
   the_window TEXT NOT NULL,
   price FLOAT8 NOT NULL,
   price_then FLOAT8 NOT NULL,
+  low FLOAT8 NOT NULL,
+  high FLOAT8 NOT NULL,
   liquidity FLOAT8 NOT NULL,
   liquidity_then FLOAT8 NOT NULL,
   direct_volume_over_window FLOAT8 NOT NULL,