server: return all completed stmt diag requests

Fixes cockroachdb#80104

Previously, we only return statement diagnostics requests
that have not yet expired. Since we use the results of this
request to populate completed statement diagnostics bundles
in addition to outstanding requests, completed statement
diag bundles would disappear from the UI after the request
expired.

This commit ensures that `StatementDiagnosticsRequests`
returns all completed stmt diag requests so that we can
display the complete history of completed bundles in the UI.

Release note (bug fix): completed stmt diagnostics bundles
now persist in the UI in stmt diag bundle pages

pkg/server/statement_diagnostics_requests.go

@@ -118,7 +118,7 @@ func (s *statusServer) CancelStatementDiagnosticsReport(
 
 // StatementDiagnosticsRequests retrieves all statement diagnostics
 // requests in the `system.statement_diagnostics_requests` table that
-// have not yet expired.
+// have either completed or have not yet expired.
 func (s *statusServer) StatementDiagnosticsRequests(
 	ctx context.Context, _ *serverpb.StatementDiagnosticsReportsRequest,
 ) (*serverpb.StatementDiagnosticsReportsResponse, error) {
@@ -182,7 +182,7 @@ func (s *statusServer) StatementDiagnosticsRequests(
 			if expiresAt, ok := row[6].(*tree.DTimestampTZ); ok {
 				req.ExpiresAt = expiresAt.Time
 				// Don't return already expired requests.
-				if req.ExpiresAt.Before(timeutil.Now()) {
+				if !completed && req.ExpiresAt.Before(timeutil.Now()) {
 					continue
 				}
 			}