[flagd] Use TestContainers instead of github services / docker for e2e tests #304
Description
We can use https://dotnet.testcontainers.org/ instead of expecting users and CI to run these manually
- start TestContainers with e2e tests
- remove services from CI: https://github.com/open-feature/dotnet-sdk-contrib/blob/main/.github/workflows/ci.yml#L50-L60
Similar PR in Java: open-feature/java-sdk-contrib#860