Remove dependency on spring-boot-testcontainers

[rwinch]

Currently the project relies on TestcontainersPropertySource to create DynamicPropertyRegistry. The usage of TestcontainersPropertySource adds a dependency on spring-boot-testcontainers. This dependency does not make sense since users will likely want to use DynamicProperties without necessarily needing Testcontainers. We should see if this can be moved to a different package or consider copying the code to remove the unnecessary dependency on spring-boot-testcontainers.