fix: endless opening of tabs with update information [#1548]

Related to #1548

What

Some users have been reporting that the new tab that opens with update informations opens an ungodly amount of times. We cannot reproduce this bug, but this is an attempt at fixing it.

How

• Created a function that checks if a tab is already open in the browser and unit test it
• Use this function in the openNotificationInNewTab function. This is the one responsible for opening new tabs for update new tab notifications
• Extract the code that applies templating to URLs in the extension and unit test it

Dear QA friend

I don't know how to trigger an "update new tab notification" on the extension 😞 While we can't reproduce the bug, we must make sure that this change does not break it.