Added in preview 1 release notes (#7400)

Author: michaelgsharp

docs/release-notes/5.0-preview.1/release-5.0-preview.1.md

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+# [ML.NET](http://dot.net/ml) 5.0-preview.1
+
+## **New Features**
+- **Introducing SentencePiece Unigram Tokenizer Model** ([#7390](https://github.com/dotnet/machinelearning/pull/7390))
+- **Phi-4 Tokenizer Support** ([#7396](https://github.com/dotnet/machinelearning/pull/7396))
+
+## **Enhancements**
+- **Support O3 OpenAI model mapping** ([#7394](https://github.com/dotnet/machinelearning/pull/7394))
+
+## **Bug Fixes**
+- **Fix DateTime export to csv with culture info** ([#7358](https://github.com/dotnet/machinelearning/pull/7358)) - Thanks @asmirnov82!
+- **Moved SpecialTokens assignment after the modification to avoid "Collection Modified" error** ([#7328](https://github.com/dotnet/machinelearning/pull/7328)) - Thanks @shaltielshmid!
+- **Fix broken inheritance from DataFrameColumn class** ([#7324](https://github.com/dotnet/machinelearning/pull/7324)) - Thanks @asmirnov82!
+
+## **Build / Test updates**
+- **[main] Update dependencies from dotnet/arcade** ([#7387](https://github.com/dotnet/machinelearning/pull/7387))
+- **Update Microsoft.Extensions.AI to 9.3.0-preview.1.25114.11** ([#7388](https://github.com/dotnet/machinelearning/pull/7388))
+- **Update MSTest to latest** ([#7349](https://github.com/dotnet/machinelearning/pull/7349))
+- **[main] Update dependencies from dotnet/arcade** ([#7352](https://github.com/dotnet/machinelearning/pull/7352))
+- **Consolidate System.Numerics.Tensors dependency** ([#7356](https://github.com/dotnet/machinelearning/pull/7356)) - Thanks @asmirnov82!
+- **[main] Update dependencies from dotnet/arcade** ([#7382](https://github.com/dotnet/machinelearning/pull/7382))
+- **[main] Update dependencies from dotnet/arcade** ([#7376](https://github.com/dotnet/machinelearning/pull/7376))
+- **[main] Update dependencies from dotnet/arcade** ([#7374](https://github.com/dotnet/machinelearning/pull/7374))
+- **Net8 tests** ([#7319](https://github.com/dotnet/machinelearning/pull/7319))
+- **[main] Update dependencies from dotnet/arcade** ([#7266](https://github.com/dotnet/machinelearning/pull/7266))
+- **Update DependencyModel** ([#7338](https://github.com/dotnet/machinelearning/pull/7338))
+- **Update M.E.AI version used by Microsoft.ML.GenAI.Core** ([#7329](https://github.com/dotnet/machinelearning/pull/7329))
+- **Update System.Numerics.Tensors version** ([#7322](https://github.com/dotnet/machinelearning/pull/7322)) - Thanks @asmirnov82!
+
+## **Documentation Updates**
+- **Fix up docs for MLContext** ([#7334](https://github.com/dotnet/machinelearning/pull/7334))
+- **Some tweaks to the Microsoft.ML.Tokenizers PACKAGE.md** ([#7360](https://github.com/dotnet/machinelearning/pull/7360))
+- **[GenAI] SFT Example** ([#7316](https://github.com/dotnet/machinelearning/pull/7316))
+- **Update dynamic loading report reference** ([#7321](https://github.com/dotnet/machinelearning/pull/7321)) - Thanks @emmanuel-ferdman!
+