Move powershell code block monicker to PlatyPS

[bravo-kernel]

Because PlatyPS does not add the powershell syntax highlighting language to code blocks we are currently adding the monicker ourselves during the markdown-to-mdx transformation, see https://github.com/alt3/Docusaurus.Powershell/blob/master/Source/Private/UpdateContentCodeBlocks.ps1

Ideally... a PR should be made to update PlatyPS so we can drop this step. Green light given by the repo owner, just needs to be done (see PowerShell/platyPS#475 (comment)). Additional background info at PowerShell/platyPS#294

[bravo-kernel]

Additional info:

• Add "powershell" label to examples markdown PowerShell/platyPS#294
• Powershell moniker not added when using Powershell Core PowerShell/platyPS#475 (comment)