Seed CLI telemetry session IDs from CI workflow context - #54447

The CLI had a per-process telemetry session ID, but no first-class way to correlate multiple dotnet invocations that belong to the same CI workflow. This updates the CLI to honor DOTNET_CLI_TELEMETRY_SESSIONID as the initial session seed and documents how CI integrations can set it consistently.

• CLI session seeding

  • TelemetryClient now uses DOTNET_CLI_TELEMETRY_SESSIONID when no explicit session ID is provided.
  • This preserves existing explicit-session behavior while enabling cross-invocation correlation for workflow-scoped sessions.

• MSBuild forwarding coverage

  • Added focused tests to verify:
    • environment-seeded session IDs become TelemetryClient.CurrentSessionId
    • explicit session IDs still take precedence
    • forwarded MSBuild invocations receive the seeded DOTNET_CLI_TELEMETRY_SESSIONID

• Docs

  • Documented DOTNET_CLI_TELEMETRY_SESSIONID in telemetry docs and CLI README.
  • Added concrete GitHub Actions and Azure DevOps examples showing how to stamp a workflow/job-scoped identifier once and let subsequent dotnet invocations inherit it.

• Repo CI integration

  • Repo GitHub Actions workflow now sets:

    DOTNET_CLI_TELEMETRY_SESSIONID: gha-${{ github.repository_id }}-${{ github.run_id }}-${{ github.run_attempt }}

  • Repo AzDo pipelines now set:

    DOTNET_CLI_TELEMETRY_SESSIONID: azdo-$(System.CollectionId)-$(System.TeamProjectId)-$(Build.BuildId)

Example:

var initialSessionId = !string.IsNullOrEmpty(sessionId)
    ? sessionId
    : environmentProvider.GetEnvironmentVariable(EnvironmentVariableNames.DOTNET_CLI_TELEMETRY_SESSIONID);

CurrentSessionId ??= !string.IsNullOrEmpty(initialSessionId)
    ? initialSessionId
    : Guid.NewGuid().ToString();