fix: correct cron expression and update Node.js to v20

[qfai]

Summary

This PR fixes two issues in the nodejs-typescript-policies sample:

1. Fix cron expression bug in connections.ts

Before:

const cronExpression = `0 0 0 ${currentDate.getUTCMonth()} ${currentDate.getUTCDay()} *`;
// Result: '0 0 0 0 4 *' - Invalid! Day cannot be 0

After:

const cronExpression = `0 0 0 ${currentDate.getUTCDate()} ${currentDate.getUTCMonth() + 1} *`;
// Result: '0 0 0 15 1 *' - Valid cron expression

The issue was:

• getUTCMonth() returns 0-11, was incorrectly placed in the day position
• getUTCDay() returns day of week (0-6), was incorrectly placed in the month position
• Correct format: {second} {minute} {hour} {day} {month} {day-of-week}

2. Update Node.js version in azure.bicep

Updated WEBSITE_NODE_DEFAULT_VERSION from ~18 to ~20 since Node.js 18 is no longer supported.

Testing

• Tested locally with F5 debug, Azure Function starts successfully without cron expression errors."