Add branch field to Telegram integration

What does this MR do and why?

It adds branches_to_be_notified field to the Telegram integration.

Screenshots or screen recordings

Before	After
N/A

How to set up and validate locally

1. Checkout the bmarjanovic/add-branches-to-be-notified-to-telegram branch
2. Configure the Telegram integration (Settings/Integrations/Telegram)
3. Change the Branches for which notifications are to be sent value to All branches
4. Push the change to another branch
5. Validate that notifications are being sent 🎉

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.