docs(week 21-22): add packer, powershell (#30)

.editorconfig

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+root = true
+
+# All Files
+
+[*]
+charset = utf-8
+indent_style = tab
+indent_size = 2
+trim_trailing_whitespace = true
+# Unix-style newlines with a newline ending every file
+end_of_line = lf
+insert_final_newline = true
+
+#########################
+# File Extension Settings
+#########################
+
+[*.{yml,yaml}]
+indent_style = space
+indent_size = 2
+
+# Markdown Files
+#
+# Two spaces at the end of a line in Markdown mean "new line",
+# so trimming trailing whitespace for such files can cause breakage.
+[*.md]
+trim_trailing_whitespace = false

packer/whitespace-in-env-vars.md

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+# 'Packer - whitespace in env vars
+
+When setting [environment variables Packer](https://developer.hashicorp.com/packer/docs/provisioners/powershell#environment_vars), make sure there's no space in between.
+If there's a whitespace, Packer passes on that whitespace within the value of the env var.
+
+Using `#` as a marker, we can see what value our env var will look like:
+
+```hcl
+  provisioner "powershell" {
+    environment_vars = [
+      "ENV_VAR_WITHOUT_SPACE=${var.tmp_folder}",
+      "ENV_VAR_WITH_SPACE = ${var.tmp_folder}"
+    ]
+    inline = [
+      "$ErrorActionPreference='Stop'",
+      "Write-Host \"EnvVarWithoutSpace:#$Env:ENV_VAR_WITHOUT_SPACE\"",
+      "Write-Host \"EnvVarWithSpace:#$Env:ENV_VAR_WITH_SPACE\""
+    ]
+  }
+```
+
+output is
+
+```console
+. . .
+EnvVarWithoutSpace:#C:\tmp\packer-env-var
+EnvVarWithSpace:# C:\tmp\packer-env-var
+```
+
+Another way to deal with this is to call the `Trim` method before processing those env vars:
+
+```powershell
+# check if they exist
+$expectedEnvVars = @(
+    $env:ENV_VAR_WITHOUT_SPACE, 
+    $env:ENV_VAR_WITH_SPACE
+)
+foreach ($envVar in $expectedEnvVars) {
+    if ([string]::IsNullOrWhiteSpace($envVar)) {
+        throw "$envVar is null or is empty" 
+    }
+}
+$MyVar1 = ($env:ENV_VAR_WITHOUT_SPACE).Trim()
+$MyVar2 = ($env:ENV_VAR_WITH_SPACE).Trim()
+
+# do something with $MyVar1 and $MyVar2
+```

powershell/set-env-vars-differing-scope.md

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+# Powershell - set env vars in different scopes
+
+While trying to understand [this line](https://github.com/actions/runner-images/blob/035dc70f77d4353de9fbacd66be4f0797d4d9f62/images/win/scripts/ImageHelpers/PathHelpers.ps1#L63) from the utilities that GitHub uses for their GitHub Runners, it occurred to me that environment variables are defined in different contexts that affects how long they last.
+
+Thanks to [shellgeek](https://shellgeek.com/set-environment-variable-using-powershell/), there's a way to set the env vars in PowerShell accordingly:
+
+- Env vars for the duration of the powershell session and process:
+  `$Env:GoHugo = "C:\Hugo\bin\"`
+
+- Env var for the User account (System Settings -> Advanced -> Environment Variables -> User): 
+  `[System.Environment]::SetEnvironmentVariable('GoHugo','C:\Hugo\bin',[System.EnvironmentVariableTarget]::User)`
+
+- Env var for the machine in (System Settings -> Advanced -> Environment Variables -> System): 
+  `[System.Environment]::SetEnvironmentVariable('GoHugo','C:\Hugo\bin',[System.EnvironmentVariableTarget]::Machine)`