[FE] Handle running UI tests on localhost

[vOrigins]

Tests should be run with different parameters depending on how APIHUB UI is launched.

1. Live environment ✅
2. Local via docker compose ✅
3. Local via docker compose + dev proxy ✅

To test the "Playground" via a localhost, in playwright tests, you need to set a value for the PLAYGROUND_BACKEND_HOST environment variable, it will be used in the test to create a custom server for sending requests.

In case of using Docker Compose, this is http://host.docker.internal:8081 (protocol + value of the APIHUB_URL variable from the qubership-apihub-backend.env file). Also, you need to add the variable ALLOWED_HOSTS=host.docker.internal to the qubership-apihub-backend.env file.

In case of using docker compose + dev proxy, in addition to the previous settings, in playwright tests, you need to add the variable DEV_PROXY_MODE=true, to skip tests that cannot be executed in this mode.

These settings should be reflected in the README.

	Live environment	Docker compose	Docker compose + dev proxy
Playground tests	✔️	✔️ ALLOWED_HOSTS=host.docker.internal - in docker compose PLAYGROUND_BACKEND_HOST=http://host.docker.internal:8081 - in tests	✔️ ALLOWED_HOSTS=host.docker.internal - in docker compose PLAYGROUND_BACKEND_HOST=http://host.docker.internal:8081 - in test
Tests with rediretcs to the Agent	✔️	✔️	❌ Skipped with DEV_PROXY_MODE=true - in tests
Expand/collapse the Package page sidebar test	✔️	✔️	❌ Skipped with DEV_PROXY_MODE=true - in tests