Make TestContainersSuite public

[thomasl8]

It would be nice to be able to use this in our own mixins.

e.g. have some common set-up defined in a trait

trait PostgresSupport { self: Suite with TestContainersSuite =>
   val container = ???
}

And then we can decide if you want to use ForEachTestContainer or ForAllTestContainer depending on the actual tests.

class MyRepoSpec extends AnyFlatSpec with ForEachTestContainer with PostgresSupport