Make all functions use the default proxy(if the proxy was enabled) when no proxy specified

まず、システムプロキシを有効にし、明示的なプロキシを指定せず、示されているバージョンの PowerShellGet と PackageManagement を使用して、ps リポジトリの登録を再現します。登録リクエストと関連する関数を追跡し、プロキシ処理がどこで分岐しているかを特定します。プロキシ引数が指定されていない場合に、有効なデフォルトプロキシ経由でリポジトリの登録が成功し、影響を受ける動作のカバレッジがあることをもって完了とします。

Expected Behavior

register the ps repository successfully

Current Behavior

nothing happened

Possible Solution

when no proxy specified, then invoke the default proxy (when the proxy was enabled)
https://stackoverflow.com/questions/571429/powershell-web-requests-and-proxies

Steps to Reproduce (for bugs)

set the proxy on computer

Context

related to https://github.com/PowerShell/WindowsCompatibility/issues/45
I want to register ps repository

Your Environment

> $PSVersionTable
Name                           Value
----                           -----
PSVersion                      6.1.0
PSEdition                      Core
GitCommitId                    6.1.0
OS                             Microsoft Windows 10.0.16299
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0
> Get-Module
ModuleType Version    Name                                ExportedCommands
---------- -------    ----                                ----------------
Script     0.0        build                               {Clear-PSRepo, Compress-TestContent, Convert-TxtResourceToXml, ConvertFrom-PesterLog...}
Script     0.0        chuck                               Reset-FolderTime
Script     0.0        Get-PSGalleryApiAvailability
Manifest   6.1.0.0    Microsoft.PowerShell.Management     {Add-Content, Clear-Content, Clear-Item, Clear-ItemProperty...}
Manifest   6.1.0.0    Microsoft.PowerShell.Management     {Add-Content, Clear-Content, Clear-Item, Clear-ItemProperty...}
Manifest   6.1.0.0    Microsoft.PowerShell.Security       {ConvertFrom-SecureString, ConvertTo-SecureString, Get-Acl, Get-AuthenticodeSignature...}
Manifest   6.1.0.0    Microsoft.PowerShell.Utility        {Add-Member, Add-Type, Clear-Variable, Compare-Object...}
Manifest   6.1.0.0    Microsoft.WSMan.Management          {Connect-WSMan, Disable-WSManCredSSP, Disconnect-WSMan, Enable-WSManCredSSP...}
Script     1.1.7.2    PackageManagement                   {Find-Package, Find-PackageProvider, Get-Package, Get-PackageProvider...}
Script     1.0.0.0    posh-git                            {Add-PoshGitToProfile, Expand-GitCommand, Format-GitBranchName, Get-GitBranchStatusColor...}
Script     2.0.1      PowerShellGet                       {Find-Command, Find-DscResource, Find-Module, Find-RoleCapability...}
Script     2.0.0      PSReadLine                          {Get-PSReadLineKeyHandler, Get-PSReadLineOption, Remove-PSReadLineKeyHandler, Set-PSReadLineKeyHandler...}
> Get-Module -ListAvailable PowerShellGet,PackageManagement
ModuleType Version    Name                                PSEdition ExportedCommands
---------- -------    ----                                --------- ----------------
Script     1.1.7.2    PackageManagement                   Desk      {Find-Package, Get-Package, Get-PackageProvider, Get-PackageSource...}
Script     1.6.7      PowerShellGet                       Desk      {Find-Command, Find-DSCResource, Find-Module, Find-RoleCapability...}
> Get-PackageProvider
Name                     Version          DynamicOptions
----                     -------          --------------
NuGet                    2.8.5.210        Destination, ExcludeVersion, Scope, SkipDependencies, Headers, FilterOnTag, Contains, AllowPrereleaseVersions, ConfigFile, SkipValidate
PowerShellGet            1.6.7.0          PackageManagementProvider, Type, Scope, AllowClobber, SkipPublisherCheck, InstallUpdate, NoPathUpdate, AllowPrereleaseVersions, Filter, Tag, Includes, DscResource, RoleCapability, Command, Ac...
> Get-PackageProvider -ListAvailable
Name                     Version          DynamicOptions
----                     -------          --------------
NuGet                    2.8.5.210        Destination, ExcludeVersion, Scope, SkipDependencies, Headers, FilterOnTag, Contains, AllowPrereleaseVersions, ConfigFile, SkipValidate
PowerShellGet            1.6.7.0          PackageManagementProvider, Type, Scope, AllowClobber, SkipPublisherCheck, InstallUpdate, NoPathUpdate, AllowPrereleaseVersions, Filter, Tag, Includes, DscResource, RoleCapability, Command, Ac...