(#41) Add office use only section to PR template

[corbob]

Description Of Changes

This commit adds to the PR template to include some "office use only"
sections. These sections are intended for Chocolatey team members to
ensure we cover our bases with our PRs.

This also adds a section to allow explanation for a Draft PR, so we
don't need to go looking through the PR to understand why it's in a
draft state.

Motivation and Context

This will allow us to ensure we capture things we need to do with most of our PRs, and provide context for why a PR might be in draft status.

Testing

I have not done testing as this is just an update to the template used for PRs. I have applied the new section to this PR though to get an idea of what it would look like...

Operating Systems Testing

N/A

Change Types Made

• Bug fix (non-breaking change).
• Feature / Enhancement (non-breaking change).
• Breaking change (fix or feature that could cause existing functionality to change).
• Documentation changes.
• PowerShell code changes.

Change Checklist

• Requires a change to the documentation.
• Documentation has been updated.
• Tests to cover my changes, have been added.
• All new and existing tests passed?
• PowerShell code changes: PowerShell v3 compatibility checked?

Related Issue

Fixes #41

Reason for Draft Status

N/A

Chocolatey Team Pre-merge Checklist

This section is for Chocolatey team members to validate things prior to merge. Each section should have only one option selected. Any option marked with (*) should have an individual comment with further details.

Corresponding Product Changes

• This PR affects other Chocolatey products that may need corresponding changes. (eg: Chocolatey GUI, Chocolatey Licensed Extension)
• This PR does not affect other Chocolatey products that may need corresponding changes. (eg: Chocolatey GUI, Chocolatey Licensed Extension)

Milestone Tracking

• This PR is attached to an issue that is attached to a milestone.
• This PR is not attached to an issue, so it has been attached to a milestone.
• This PR does not need to be attached to a milestone. (*)

Inter-branch Porting

• This PR affects changes that will need to be ported to other branches. (*)
• This PR does not affect changes that will need to be ported to other branches.

Pester Test Specifics

• This PR affects Pester tests unrelated to Chocolatey CLI changes that need to be ported to the master branch.
• This PR affects Pester tests due to build changes and needs to be ported to both master and support branches.