Bitbucket should not create multiple application links to the same URL

Steps to reproduce:

1. Install a Bamboo instance
2. Connect it to Bitbucket through an application link
3. Stop the instance
4. Install another Bamboo instance with the exact same Base URL used in step 1
5. Try to connect it to Bitbucket through an application link

Expected results:

An error is thrown telling the user that another application link to the same URL already exists

Actual results:

A second application link endpoint is created (probably because the server ID is different and no other checking is performed)