Fix integration tests run

[dmilov]

• Implement wait test HTTP server to start in BeforeAll to make sure integration test will reach the server when it is ready
• Fix time formatting in binary content mode to use 3 digits fraction of the seconds in ISO 8601 format. This way the time is formatted the same way as the C# SDK formats it for structure mode.

Testing done:

• Github Action Integration tests on ubuntu-latest https://github.com/dmilov/sdk-powershell/runs/2446579405?check_suite_focus=true

• Local testing with all tests

> .\build.ps1
[6:50:08 PM] INFO: Publish CloudEvents.Sdk Module to 'C:\git-repos\github\sdk-powershell\CloudEvents.Sdk'
Microsoft (R) Build Engine version 16.9.0+57a23d249 for .NET                                                            Copyright (C) Microsoft Corporation. All rights reserved.                                                                                                                                                                                         Determining projects to restore...                                                                                      All projects are up-to-date for restore.
  CloudEventsPowerShell -> C:\git-repos\github\sdk-powershell\src\CloudEventsPowerShell\bin\Release\netstandard2.0\CloudEventsPowerShell.dll
  CloudEventsPowerShell -> C:\git-repos\github\sdk-powershell\CloudEvents.Sdk\
[6:50:09 PM] INFO: Run unit tests

Starting discovery in 9 files.
Discovery finished in 1.18s.
[+] C:\git-repos\github\sdk-powershell\test\unit\ConvertFrom-HttpMessage.Tests.ps1 2.12s (813ms|1.03s)
[+] C:\git-repos\github\sdk-powershell\test\unit\ConvertTo-HttpMessage.Tests.ps1 615ms (200ms|287ms)
[+] C:\git-repos\github\sdk-powershell\test\unit\New-CloudEvent.Tests.ps1 462ms (156ms|204ms)
[+] C:\git-repos\github\sdk-powershell\test\unit\Read-CloudEventData.Tests.ps1 399ms (99ms|198ms)
[+] C:\git-repos\github\sdk-powershell\test\unit\Read-CloudEventJsonData.Tests.ps1 508ms (218ms|189ms)
[+] C:\git-repos\github\sdk-powershell\test\unit\Read-CloudEventXmlData.Tests.ps1 626ms (342ms|182ms)
[+] C:\git-repos\github\sdk-powershell\test\unit\Set-CloudEventData.Tests.ps1 870ms (453ms|286ms)
[+] C:\git-repos\github\sdk-powershell\test\unit\Set-CloudEventJsonData.Tests.ps1 488ms (174ms|212ms)
[+] C:\git-repos\github\sdk-powershell\test\unit\Set-CloudEventXmlData.Tests.ps1 641ms (344ms|197ms)
Tests completed in 6.79s
Tests Passed: 28, Failed: 0, Skipped: 0 NotRun: 0
[6:50:18 PM] INFO: Run integration tests

Starting discovery in 1 files.
Discovery finished in 269ms.
[+] C:\git-repos\github\sdk-powershell\test\integration\HttpIntegration.Tests.ps1 3.79s (2.47s|1.09s)
Tests completed in 3.86s
Tests Passed: 5, Failed: 0, Skipped: 0 NotRun: 0

[embano1]

Thx!