Enable health check for Tracker container

[josecelano]

After merging torrust/torrust-tracker#512 the Tracker container has a HEALTHCHECK. We can use it:

• Here: https://github.com/torrust/torrust-index/blob/develop/contrib/dev-tools/container/e2e/mysql/run-e2e-tests.sh#L32-L33
• And here: https://github.com/torrust/torrust-index/blob/develop/contrib/dev-tools/container/e2e/sqlite/run-e2e-tests.sh#L33-L34