New/Update-GitHubRepository: Add Support for delete_branch_on_merge API Property

[X-Guardian]

Description

The GitHub Create/Update Repository APIs have a delete_branch_on_merge property which is not currently supported by the New-GitHubRepository and Update-GitHubRepository functions. This allows automatically deleting of head branches when pull requests are merged within the repo.

Proposal

Add a DeleteBranchOnMerge switch parameter to both functions to add support for this feature.

API Detail

delete_branch_on_merge | boolean | Either `true` to allow automatically deleting head branches when pull requests are merged, or `false` to prevent automatic deletion. Default: `false`.

[HowardWolosky]

Makes sense to me. We should also make sure that there aren't any other options that the functions are missing, for completness.

[X-Guardian]

Looking at the GitHub Repositories REST API Docs, the Create/Update APIs also have the visibility and is_template parameters which are not currently supported by the GitHubRepository functions.

API Detail

Parameter	Type	Description
visibility	string	Can be public or private. If your organization is associated with an enterprise account using GitHub Enterprise Cloud or GitHub Enterprise Server 2.20+, visibility can also be internal. For more information, see "Creating an internal repository" in the GitHub Help documentation. The visibility parameter overrides the private parameter when you use both parameters with the nebula-preview preview header.
is_template	boolean	Either true to make this repo available as a template repository or false to prevent it. Default: false.