opt: remove uniqueness checks for gen_random_uuid()

This commit removes uniqueness checks for UUID columns that are set
to gen_random_uuid(), because uniqueness can be sufficiently guaranteed
by randomness. The probability of collision when using gen_random_uuid()
is extremely low. If users still want the checks, however, they can set
sql.optimizer.uniqueness_checks_for_gen_random_uuid.enabled, a new cluster
setting, to true. By default the setting is false.

Fixes #57790

Release justification: This commit is a low-risk update to new functionality.

Release note (sql change): Added a new cluster setting
sql.optimizer.uniqueness_checks_for_gen_random_uuid.enabled, which controls
creation of uniqueness checks for UUID columns set to gen_random_uuid().
When enabled, uniqueness checks will be added for the UUID column if it
has a unique constraint that cannot be enforced by an index. When disabled,
no uniqueness checks are planned for these columns, and uniqueness is
assumed due to the near-zero collision probability of gen_random_uuid()

docs/generated/settings/settings-for-tenants.txt

@@ -81,6 +81,7 @@ sql.metrics.statement_details.plan_collection.period	duration	5m0s	the time unti
 sql.metrics.statement_details.threshold	duration	0s	minimum execution time to cause statement statistics to be collected. If configured, no transaction stats are collected.
 sql.metrics.transaction_details.enabled	boolean	true	collect per-application transaction statistics
 sql.notices.enabled	boolean	true	enable notices in the server/client protocol being sent
+sql.optimizer.uniqueness_checks_for_gen_random_uuid.enabled	boolean	false	if enabled, uniqueness checks may be planned for mutations of UUID columns updated with gen_random_uuid(); otherwise, uniqueness is assumed due to near-zero collision probability
 sql.spatial.experimental_box2d_comparison_operators.enabled	boolean	false	enables the use of certain experimental box2d comparison operators
 sql.stats.automatic_collection.enabled	boolean	true	automatic statistics collection mode
 sql.stats.automatic_collection.fraction_stale_rows	float	0.2	target fraction of stale rows per table that will trigger a statistics refresh

docs/generated/settings/settings.html

@@ -83,6 +83,7 @@
 <tr><td><code>sql.metrics.statement_details.threshold</code></td><td>duration</td><td><code>0s</code></td><td>minimum execution time to cause statement statistics to be collected. If configured, no transaction stats are collected.</td></tr>
 <tr><td><code>sql.metrics.transaction_details.enabled</code></td><td>boolean</td><td><code>true</code></td><td>collect per-application transaction statistics</td></tr>
 <tr><td><code>sql.notices.enabled</code></td><td>boolean</td><td><code>true</code></td><td>enable notices in the server/client protocol being sent</td></tr>
+<tr><td><code>sql.optimizer.uniqueness_checks_for_gen_random_uuid.enabled</code></td><td>boolean</td><td><code>false</code></td><td>if enabled, uniqueness checks may be planned for mutations of UUID columns updated with gen_random_uuid(); otherwise, uniqueness is assumed due to near-zero collision probability</td></tr>
 <tr><td><code>sql.spatial.experimental_box2d_comparison_operators.enabled</code></td><td>boolean</td><td><code>false</code></td><td>enables the use of certain experimental box2d comparison operators</td></tr>
 <tr><td><code>sql.stats.automatic_collection.enabled</code></td><td>boolean</td><td><code>true</code></td><td>automatic statistics collection mode</td></tr>
 <tr><td><code>sql.stats.automatic_collection.fraction_stale_rows</code></td><td>float</td><td><code>0.2</code></td><td>target fraction of stale rows per table that will trigger a statistics refresh</td></tr>

pkg/sql/logictest/testdata/logic_test/unique

@@ -104,11 +104,19 @@ CREATE TABLE uniq_computed_pk (
 )
 
 statement ok
-CREATE TABLE other (k INT, v INT, w INT NOT NULL, x INT, y INT)
+CREATE TABLE uniq_uuid (
+  id1 UUID,
+  id2 UUID,
+  UNIQUE WITHOUT INDEX (id1),
+  UNIQUE WITHOUT INDEX (id2)
+)
+
+statement ok
+CREATE TABLE other (k INT, v INT, w INT NOT NULL, x INT, y INT, u UUID)
 
 # Insert some data into the other table.
 statement ok
-INSERT INTO other VALUES (10, 10, 1, 1, 1)
+INSERT INTO other VALUES (10, 10, 1, 1, 1, '8597b0eb-7b89-4857-858a-fabf86f6a3ac')
 
 
 # -- Tests with INSERT --
@@ -361,6 +369,15 @@ i  s  d    c_i_expr  c_s  c_d  c_d_expr
 1  a  1.0  bar       a    1.0  1.0
 2  b  2.0  bar       b    2.0  2.0
 
+# Insert a couple of rows into a table with UUID columns.
+statement ok
+INSERT INTO uniq_uuid (id1, id2) SELECT gen_random_uuid(), '8597b0eb-7b89-4857-858a-fabf86f6a3ac'
+
+# We can catch uniqueness violations on UUID columns set to a value other than
+# gen_random_uuid().
+statement error pgcode 23505 pq: duplicate key value violates unique constraint "unique_id2"\nDETAIL: Key \(id2\)=\('8597b0eb-7b89-4857-858a-fabf86f6a3ac'\) already exists\.
+INSERT INTO uniq_uuid (id1, id2) SELECT gen_random_uuid(), u FROM other
+
 
 # -- Tests with UPDATE --
 subtest Update