feat: Enable FDv2 public experimental support.

[kinyoklion]

BEGIN_COMMIT_OVERRIDE
feat(experimental): Release EAP support for FDv2 data system.
END_COMMIT_OVERRIDE

Note

Enables public experimental configuration of the FDv2 data system.

• Exposes Components.DataSystem(), Configuration.DataSystem, and ConfigurationBuilder.DataSystem(...) publicly
• Makes DataSystemBuilder, DataSystemComponents, DataSystemModes, and DataSystemConfiguration public, including PersistentStore(...) on DataSystemBuilder
• Publishes FDv2 data source builders: FDv2PollingDataSourceBuilder and FDv2StreamingDataSourceBuilder
• Exposes selector APIs: ISelectorSource and LdClientContext.SelectorSource
• Test updates: assert Initialized is true for FDv2 data sources
• Version bump in LaunchDarkly.ServerSdk.csproj to 8.11.0-beta.1

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[kinyoklion]

Will hold merging until we are ready to release.