[CAL-4951] Add a testing/dry run banner in dry-run mode of booking(identified isBookingDryRun)

[hariombalhara]

Intention is to clearly show to the user when he lands on the page that it is a test page or a dry run booking page.

_{From SyncLinear.com | CAL-4951}

[vaibhav0725]

Approach For Resolving The Issue

1. creating a reusable banner [DryRunBanner.tsx] as a component for the frontend section (ui)
2. next, implementing a flag [isBookingDryRun] keeping it false initially
3. fetching value[true/false : accordingly] for it through the api route, and display/not display the banner accordingly
4. creating a backend api to support all the above

Lemme Know

• if I am understanding the issue correctly
• and if yes, then please provide me some insights about how to proceed