Update function template documentation and enhance GitHub context ass… (#209)

## Description

This pull request includes changes to the
`tools/utilities/New-FunctionTemplate.ps1` file to update documentation
and improve context assertion.

### Function template update

* `tools/utilities/New-FunctionTemplate.ps1`
* Replaced the general notes section with a title and link.
[[1]](diffhunk://#diff-744fac7ebd78c04d74015c27b179c4843ba0c23ae76ffc8957c4bb8ec022fe78L13-R13)
* Added the `Assert-GitHubContext` function to assert a GitHub contexts
authentication types.
[[2]](diffhunk://#diff-744fac7ebd78c04d74015c27b179c4843ba0c23ae76ffc8957c4bb8ec022fe78L34-R35)
  * Fixes #186

## Type of change

<!-- Use the check-boxes [x] on the options that are relevant. -->

- [ ] 📖 [Docs]
- [ ] 🪲 [Fix]
- [x] 🩹 [Patch]
- [ ] ⚠️ [Security fix]
- [ ] 🚀 [Feature]
- [ ] 🌟 [Breaking change]

## Checklist

<!-- Use the check-boxes [x] on the options that are relevant. -->

- [x] I have performed a self-review of my own code
- [x] I have commented my code, particularly in hard-to-understand areas

Author: MariusStorhaug

tools/utilities/New-FunctionTemplate.ps1

@@ -10,7 +10,7 @@
         An example
 
         .NOTES
-        General notes
+        [Ttle](link)
     #>
     [CmdletBinding(SupportsShouldProcess)]
     param(
@@ -31,8 +31,8 @@
     begin {
         $commandName = $MyInvocation.MyCommand.Name
         Write-Debug "[$commandName] - Start"
-
         $Context = Resolve-GitHubContext -Context $Context
+        Assert-GitHubContext -Context $Context -AuthType IAT, PAT, UAT
 
         if ([string]::IsNullOrEmpty($Enterprise)) {
             $Enterprise = $Context.Enterprise