Document release process

[andyleejordan]

Over the last few months I've revamped the release process and it is now significantly easier (though there is, of course, still room for improvement). My notes are just on my computer right now and I'd instead like to properly document them in the repo for myself and potential future maintainers.

[rjmholt]

Related to #2286

[andyleejordan]

Import-Module ./tools/ReleaseTools.psm1
Update-Changelog -RepositoryName PowerShellEditorServices -Version <version>
Update-Changelog -RepositoryName vscode-powershell -Version <version>
# Amend changelog as necessary
Update-Version -RepositoryName PowerShellEditorServices
Update-Version -RepositoryName vscode-powershell
# Push branches to GitHub and ADO
# Open PRs for review and merge
# Download and test assets (assert correct PSES is included)
# Rename VSIX correctly
New-DraftRelease -RepositoryName PowerShellEditorServices
New-DraftRelease -RepositoryName vscode-powershell
# Push Git tags for each repo
# Upload PowerShellEditorServices.zip (for other extensions)
# Upload VSIX and Install-VSCode.ps1
# Publish draft releases
vsce publish --packagePath ./PowerShell-Preview-2021.4.2.vsix
# Update Install-VSCode.ps1 on marketplace
Publish-Script -Path ./Install-VSCode.ps1 -NuGetApiKey (Get-Secret "PowerShell Gallery API Key" -AsPlainText)