sql: add plan gist to sampled query telemetry log

Partially resolves: #71328

This change adds a plan gist field to the sampled query telemetry log.
The plan gist is written as a base64 encoded string.

Release note (sql change): The sampled query telemetry log now includes
a plan gist field. The plan gist field provides a compact representation
of a logical plan for the sampled query, the field is written as a
base64 encoded string.

docs/generated/eventlog.md

@@ -2458,6 +2458,7 @@ contains common SQL event/execution details.
 | `SkippedQueries` | skipped_queries indicate how many SQL statements were not considered for sampling prior to this one. If the field is omitted, or its value is zero, this indicates that no statement was omitted since the last event. | no |
 | `CostEstimate` | Cost of the query as estimated by the optimizer. | no |
 | `Distribution` | The distribution of the DistSQL query plan (local, full, or partial). | no |
+| `PlanGist` | The query's plan gist bytes as a base64 encoded string. | no |
 
 
 #### Common fields

pkg/sql/exec_log.go

@@ -389,6 +389,7 @@ func (p *planner) maybeLogStatementInternal(
 				SkippedQueries:       skippedQueries,
 				CostEstimate:         p.curPlan.instrumentation.costEstimate,
 				Distribution:         p.curPlan.instrumentation.distribution.String(),
+				PlanGist:             p.curPlan.instrumentation.planGist.String(),
 			}})
 		} else {
 			telemetryMetrics.incSkippedQueryCount()

pkg/sql/telemetry_logging_test.go

@@ -231,6 +231,11 @@ func TestTelemetryLogging(t *testing.T) {
 				if !distRe.MatchString(e.Message) {
 					t.Errorf("expected to find Distribution but none was found")
 				}
+				// Match plan gist on any non-empty string value.
+				planGist := regexp.MustCompile("\"PlanGist\":(\"\\S+\")")
+				if !planGist.MatchString(e.Message) {
+					t.Errorf("expected to find PlanGist but none was found in: %s", e.Message)
+				}
 				for _, eTag := range tc.expectedUnredactedTags {
 					for _, tag := range strings.Split(e.Tags, ",") {
 						kv := strings.Split(tag, "=")

pkg/util/log/eventpb/telemetry.proto

@@ -43,6 +43,9 @@ message SampledQuery {
 
   // The distribution of the DistSQL query plan (local, full, or partial).
   string distribution = 6 [(gogoproto.jsontag) = ",omitempty", (gogoproto.moretags) = "redact:\"nonsensitive\""];
+
+  // The query's plan gist bytes as a base64 encoded string.
+  string plan_gist = 7 [(gogoproto.jsontag) = ',omitempty', (gogoproto.moretags) = "redact:\"nonsensitive\""];
 }
 
 // CapturedIndexUsageStats