[Feature Request]: Align Join-Path usage throughout PS scripts

[eriqua]

Description

Join-Path cmdlet is massively used throughout PS scripts to e.g. load functions or retrieve file paths. We should align all usages to avoid including directory separators (/ or \)

Example of intended usage . (Join-Path '$(System.DefaultWorkingDirectory)' 'utilities' 'pipelines' 'sharedScripts' 'Set-EnvironmentOnAgent.ps1')

Example of usage to align as above Import-Module (Join-Path $PSScriptRoot 'helper\helper.psm1') -Force --> Import-Module (Join-Path $PSScriptRoot 'helper' 'helper.psm1') -Force . (Join-Path $PSScriptRoot './helper/Convert-TokenInFile.ps1') --> . (Join-Path $PSScriptRoot 'helper' 'Convert-TokenInFile.ps1')