Introduce query timeout configuration (#2157)

## Summary

Implements configurable query execution timeout controls to prevent
poorly optimized or excessive queries from consuming excessive server
resources, causing performance degradation, or crashing the Zabbix
server.

Fixes: https://github.com/grafana/oss-big-tent-squad/issues/127

## Problem

Previously, the plugin only had an HTTP connection timeout (`timeout`)
that controlled individual API request timeouts. However, a complete
query execution could involve multiple API calls and run indefinitely if
not properly controlled, potentially causing resource exhaustion.

## Solution

Added a new `queryTimeout` setting that enforces a maximum execution
time for entire database queries initiated by the plugin. Queries
exceeding this limit are automatically terminated with proper error
handling and logging.

## Testing

1. Configure a datasource with `queryTimeout` set to a low value (e.g.,
5 seconds)
2. Execute a query that would normally take longer than the timeout
3. Verify that:
   - Query is terminated after the timeout period
   - Error message indicates timeout occurred
   - Logs contain timeout warning with query details
   - Other queries in the same request continue to execute

## Notes

- `queryTimeout` is separate from `timeout` (HTTP connection timeout)
- `queryTimeout` applies to the entire query execution, which may
involve multiple API calls
- Default value of 60 seconds ensures reasonable protection while
allowing normal queries to complete
- Timeout errors are logged with query refId, queryType, timeout
duration, and datasourceId for troubleshooting

pkg/settings/settings_test.go

@@ -0,0 +1,104 @@
+package settings
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestParseTimeoutValue(t *testing.T) {
+	tests := []struct {
+		name         string
+		value        interface{}
+		defaultValue int64
+		fieldName    string
+		want         int64
+		wantErr      bool
+	}{
+		{
+			name:         "valid string",
+			value:        "45",
+			defaultValue: 30,
+			fieldName:    "timeout",
+			want:         45,
+			wantErr:      false,
+		},
+		{
+			name:         "empty string returns default",
+			value:        "",
+			defaultValue: 30,
+			fieldName:    "timeout",
+			want:         30,
+			wantErr:      false,
+		},
+		{
+			name:         "invalid string returns error",
+			value:        "not-a-number",
+			defaultValue: 30,
+			fieldName:    "timeout",
+			want:         0,
+			wantErr:      true,
+		},
+		{
+			name:         "float64 value",
+			value:        float64(60),
+			defaultValue: 30,
+			fieldName:    "timeout",
+			want:         60,
+			wantErr:      false,
+		},
+		{
+			name:         "int64 value",
+			value:        int64(90),
+			defaultValue: 30,
+			fieldName:    "timeout",
+			want:         90,
+			wantErr:      false,
+		},
+		{
+			name:         "int value",
+			value:        int(120),
+			defaultValue: 30,
+			fieldName:    "timeout",
+			want:         120,
+			wantErr:      false,
+		},
+		{
+			name:         "nil returns default",
+			value:        nil,
+			defaultValue: 30,
+			fieldName:    "timeout",
+			want:         30,
+			wantErr:      false,
+		},
+		{
+			name:         "unknown type returns default",
+			value:        []string{"invalid"},
+			defaultValue: 60,
+			fieldName:    "queryTimeout",
+			want:         60,
+			wantErr:      false,
+		},
+		{
+			name:         "zero string value",
+			value:        "0",
+			defaultValue: 30,
+			fieldName:    "timeout",
+			want:         0,
+			wantErr:      false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := parseTimeoutValue(tt.value, tt.defaultValue, tt.fieldName)
+			if tt.wantErr {
+				assert.Error(t, err)
+				assert.Contains(t, err.Error(), tt.fieldName)
+			} else {
+				assert.NoError(t, err)
+				assert.Equal(t, tt.want, got)
+			}
+		})
+	}
+}