Test: simultaneous creation of legacy and modern endpoints relations

[BalabaDmitri]

Test cases

1. Deploy, relate modern endpoint, relate leagacy nedpoint, check status application, remove modern endpoint, check status application
2. Deploy, relate modern endpoint, relate leagacy nedpoint, check status application, remove legacy endpoint, check status application

Implementation

Charm goes into a "blocked" state, when creating a simultaneous relation legacy and modern endpoints.

[github-actions]

https://warthogs.atlassian.net/browse/DPE-4106

[taurus-forever]

The test merged, closing the issue.
Thank you for the contribution!