feat: Require explicit container image in Testcontainers.Xunit#1612

HofmeisterAn merged 3 commits intotestcontainers:developtestcontainers/testcontainers-dotnet:developfrom

0xced:feature/Testcontainers.Xunit-explicit-builder0xced/testcontainers-dotnet:feature/Testcontainers.Xunit-explicit-builderCopy head branch name to clipboard