feat: add TravelContainer class, Firebase dependency and unit tests

[appellet]

• feat: add TravelContainer class, Firebase dependency and unit tests

• Added TravelContainer data class and related classes (Location, Participant, Role).

• Added unit tests for TravelContainer.

• Added Firebase dependency to the project.

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud